Auto merge of #25273 - servo:fixedpos, r=nox

 Layout `position: fixed` in the initial containing block

24 files changed, 549 insertions, 401 deletions

diff --git a/Cargo.lock b/Cargo.lock
index 51a325d4ffa..418864bc117 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -4219,9 +4219,9 @@ dependencies = [
 
 [[package]]
 name = "rayon_croissant"
-version = "0.1.1"
+version = "0.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5b725e815f3aa08718063883a75003336889debafe2f8fa67fbe91563ddc4efa"
+checksum = "3e4aafda434bd10fec689858e2b1d713d0b784b1e60df3761ac8fa727d7e8e27"
 dependencies = [
  "moite_moite",
  "rayon",
diff --git a/components/layout_2020/Cargo.toml b/components/layout_2020/Cargo.toml
index 5a28da8d9ee..1d76d00af79 100644
--- a/components/layout_2020/Cargo.toml
+++ b/components/layout_2020/Cargo.toml
@@ -25,7 +25,7 @@ msg = {path = "../msg"}
 net_traits = {path = "../net_traits"}
 range = {path = "../range"}
 rayon = "1"
-rayon_croissant = "0.1.1"
+rayon_croissant = "0.2.0"
 script_layout_interface = {path = "../script_layout_interface"}
 script_traits = {path = "../script_traits"}
 serde = "1.0"
diff --git a/components/layout_2020/flow/construct.rs b/components/layout_2020/flow/construct.rs
index 4a397add2c3..25b401e5592 100644
--- a/components/layout_2020/flow/construct.rs
+++ b/components/layout_2020/flow/construct.rs
@@ -172,14 +172,6 @@ impl BlockContainer {
             contains_floats: ContainsFloats,
             outer_content_sizes_of_children: ContentSizes,
         }
-        impl Default for Accumulator {
-            fn default() -> Self {
-                Self {
-                    contains_floats: ContainsFloats::No,
-                    outer_content_sizes_of_children: ContentSizes::zero(),
-                }
-            }
-        }
         let mut acc = Accumulator {
             contains_floats: builder.contains_floats,
             outer_content_sizes_of_children: ContentSizes::zero(),
@@ -199,13 +191,21 @@ impl BlockContainer {
             builder
                 .block_level_boxes
                 .into_par_iter()
-                .mapfold_reduce_into(&mut acc, mapfold, |left, right| {
-                    left.contains_floats |= right.contains_floats;
-                    if content_sizes.requests_inline() {
-                        left.outer_content_sizes_of_children
-                            .max_assign(&right.outer_content_sizes_of_children)
-                    }
-                })
+                .mapfold_reduce_into(
+                    &mut acc,
+                    mapfold,
+                    || Accumulator {
+                        contains_floats: ContainsFloats::No,
+                        outer_content_sizes_of_children: ContentSizes::zero(),
+                    },
+                    |left, right| {
+                        left.contains_floats |= right.contains_floats;
+                        if content_sizes.requests_inline() {
+                            left.outer_content_sizes_of_children
+                                .max_assign(&right.outer_content_sizes_of_children)
+                        }
+                    },
+                )
                 .collect()
         } else {
             builder
diff --git a/components/layout_2020/flow/inline.rs b/components/layout_2020/flow/inline.rs
index c4b760275d9..93d7d6f8bdc 100644
--- a/components/layout_2020/flow/inline.rs
+++ b/components/layout_2020/flow/inline.rs
@@ -9,10 +9,10 @@ use crate::formatting_contexts::IndependentFormattingContext;
 use crate::fragments::CollapsedBlockMargins;
 use crate::fragments::{AnonymousFragment, BoxFragment, Fragment, TextFragment};
 use crate::geom::flow_relative::{Rect, Sides, Vec2};
-use crate::positioned::{AbsolutelyPositionedBox, AbsolutelyPositionedFragment};
+use crate::positioned::{relative_adjustement, AbsolutelyPositionedBox, PositioningContext};
 use crate::sizing::ContentSizes;
 use crate::style_ext::{ComputedValuesExt, Display, DisplayGeneratingBox, DisplayOutside};
-use crate::{relative_adjustement, ContainingBlock};
+use crate::ContainingBlock;
 use app_units::Au;
 use gfx::text::text_run::GlyphRun;
 use servo_arc::Arc;
@@ -68,9 +68,9 @@ struct PartialInlineBoxFragment<'box_tree> {
     parent_nesting_level: InlineNestingLevelState<'box_tree>,
 }
 
-struct InlineFormattingContextState<'box_tree, 'a> {
-    absolutely_positioned_fragments: &'a mut Vec<AbsolutelyPositionedFragment<'box_tree>>,
-    containing_block: &'a ContainingBlock<'a>,
+struct InlineFormattingContextState<'box_tree, 'a, 'b> {
+    positioning_context: &'a mut PositioningContext<'box_tree>,
+    containing_block: &'b ContainingBlock<'b>,
     lines: Lines,
     inline_position: Length,
     partial_inline_boxes_stack: Vec<PartialInlineBoxFragment<'box_tree>>,
@@ -195,12 +195,12 @@ impl InlineFormattingContext {
     pub(super) fn layout<'a>(
         &'a self,
         layout_context: &LayoutContext,
+        positioning_context: &mut PositioningContext<'a>,
         containing_block: &ContainingBlock,
         tree_rank: usize,
-        absolutely_positioned_fragments: &mut Vec<AbsolutelyPositionedFragment<'a>>,
     ) -> FlowLayout {
         let mut ifc = InlineFormattingContextState {
-            absolutely_positioned_fragments,
+            positioning_context,
             containing_block,
             partial_inline_boxes_stack: Vec::new(),
             lines: Lines {
@@ -244,7 +244,7 @@ impl InlineFormattingContext {
                                     panic!("display:none does not generate an abspos box")
                                 },
                             };
-                        ifc.absolutely_positioned_fragments
+                        ifc.positioning_context
                             .push(box_.layout(initial_start_corner, tree_rank));
                     },
                     InlineLevelBox::OutOfFlowFloatBox(_box_) => {
@@ -346,7 +346,7 @@ impl Lines {
 impl InlineBox {
     fn start_layout<'box_tree>(
         &'box_tree self,
-        ifc: &mut InlineFormattingContextState<'box_tree, '_>,
+        ifc: &mut InlineFormattingContextState<'box_tree, '_, '_>,
     ) -> PartialInlineBoxFragment<'box_tree> {
         let style = self.style.clone();
         let cbis = ifc.containing_block.inline_size;
@@ -367,11 +367,9 @@ impl InlineBox {
             block: padding.block_start + border.block_start + margin.block_start,
             inline: ifc.inline_position - ifc.current_nesting_level.inline_start,
         };
-        start_corner += &relative_adjustement(
-            &style,
-            ifc.containing_block.inline_size,
-            ifc.containing_block.block_size,
-        );
+        if style.clone_position().is_relative() {
+            start_corner += &relative_adjustement(&style, ifc.containing_block)
+        }
         PartialInlineBoxFragment {
             style,
             start_corner,
@@ -440,7 +438,7 @@ impl<'box_tree> PartialInlineBoxFragment<'box_tree> {
 
 fn layout_atomic<'box_tree>(
     layout_context: &LayoutContext,
-    ifc: &mut InlineFormattingContextState<'box_tree, '_>,
+    ifc: &mut InlineFormattingContextState<'box_tree, '_, '_>,
     atomic: &'box_tree IndependentFormattingContext,
 ) {
     let cbis = ifc.containing_block.inline_size;
@@ -457,11 +455,9 @@ fn layout_atomic<'box_tree>(
         block: pbm.block_start,
         inline: ifc.inline_position - ifc.current_nesting_level.inline_start,
     };
-    start_corner += &relative_adjustement(
-        &atomic.style,
-        ifc.containing_block.inline_size,
-        ifc.containing_block.block_size,
-    );
+    if atomic.style.clone_position().is_relative() {
+        start_corner += &relative_adjustement(&atomic.style, ifc.containing_block)
+    }
 
     let fragment = match atomic.as_replaced() {
         Ok(replaced) => {
@@ -521,9 +517,9 @@ fn layout_atomic<'box_tree>(
             // FIXME: Do we need to call `adjust_static_positions` somewhere near here?
             let independent_layout = non_replaced.layout(
                 layout_context,
+                ifc.positioning_context,
                 &containing_block_for_children,
                 dummy_tree_rank,
-                ifc.absolutely_positioned_fragments,
             );
 
             // https://drafts.csswg.org/css2/visudet.html#block-root-margin
diff --git a/components/layout_2020/flow/mod.rs b/components/layout_2020/flow/mod.rs
index 3e45defb365..64f87ea09d0 100644
--- a/components/layout_2020/flow/mod.rs
+++ b/components/layout_2020/flow/mod.rs
@@ -7,19 +7,17 @@
 use crate::context::LayoutContext;
 use crate::flow::float::{FloatBox, FloatContext};
 use crate::flow::inline::InlineFormattingContext;
-use crate::formatting_contexts::{IndependentFormattingContext, IndependentLayout};
+use crate::formatting_contexts::{IndependentFormattingContext, IndependentLayout, NonReplacedIFC};
 use crate::fragments::{AnonymousFragment, BoxFragment, Fragment};
 use crate::fragments::{CollapsedBlockMargins, CollapsedMargin};
 use crate::geom::flow_relative::{Rect, Sides, Vec2};
-use crate::positioned::adjust_static_positions;
-use crate::positioned::{AbsolutelyPositionedBox, AbsolutelyPositionedFragment};
+use crate::positioned::{AbsolutelyPositionedBox, PositioningContext};
 use crate::replaced::ReplacedContent;
 use crate::style_ext::ComputedValuesExt;
-use crate::{relative_adjustement, ContainingBlock};
+use crate::ContainingBlock;
 use rayon::iter::{IndexedParallelIterator, IntoParallelRefIterator, ParallelIterator};
 use rayon_croissant::ParallelIteratorExt;
 use servo_arc::Arc;
-use style::computed_values::position::T as Position;
 use style::properties::ComputedValues;
 use style::values::computed::{Length, LengthOrAuto};
 use style::Zero;
@@ -67,9 +65,9 @@ impl BlockFormattingContext {
     pub(super) fn layout<'a>(
         &'a self,
         layout_context: &LayoutContext,
+        positioning_context: &mut PositioningContext<'a>,
         containing_block: &ContainingBlock,
         tree_rank: usize,
-        absolutely_positioned_fragments: &mut Vec<AbsolutelyPositionedFragment<'a>>,
     ) -> IndependentLayout {
         let mut float_context;
         let float_context = if self.contains_floats {
@@ -80,9 +78,9 @@ impl BlockFormattingContext {
         };
         let flow_layout = self.contents.layout(
             layout_context,
+            positioning_context,
             containing_block,
             tree_rank,
-            absolutely_positioned_fragments,
             float_context,
             CollapsibleWithParentStartMargin(false),
         );
@@ -103,27 +101,27 @@ impl BlockContainer {
     fn layout<'a>(
         &'a self,
         layout_context: &LayoutContext,
+        positioning_context: &mut PositioningContext<'a>,
         containing_block: &ContainingBlock,
         tree_rank: usize,
-        absolutely_positioned_fragments: &mut Vec<AbsolutelyPositionedFragment<'a>>,
         float_context: Option<&mut FloatContext>,
         collapsible_with_parent_start_margin: CollapsibleWithParentStartMargin,
     ) -> FlowLayout {
         match self {
             BlockContainer::BlockLevelBoxes(child_boxes) => layout_block_level_children(
                 layout_context,
+                positioning_context,
                 child_boxes,
                 containing_block,
                 tree_rank,
-                absolutely_positioned_fragments,
                 float_context,
                 collapsible_with_parent_start_margin,
             ),
             BlockContainer::InlineFormattingContext(ifc) => ifc.layout(
                 layout_context,
+                positioning_context,
                 containing_block,
                 tree_rank,
-                absolutely_positioned_fragments,
             ),
         }
     }
@@ -131,10 +129,10 @@ impl BlockContainer {
 
 fn layout_block_level_children<'a>(
     layout_context: &LayoutContext,
+    positioning_context: &mut PositioningContext<'a>,
     child_boxes: &'a [Arc<BlockLevelBox>],
     containing_block: &ContainingBlock,
     tree_rank: usize,
-    absolutely_positioned_fragments: &mut Vec<AbsolutelyPositionedFragment<'a>>,
     mut float_context: Option<&mut FloatContext>,
     collapsible_with_parent_start_margin: CollapsibleWithParentStartMargin,
 ) -> FlowLayout {
@@ -194,7 +192,6 @@ fn layout_block_level_children<'a>(
         current_block_direction_position: Length,
     }
 
-    let abspos_so_far = absolutely_positioned_fragments.len();
     let mut placement_state = PlacementState {
         next_in_flow_margin_collapses_with_parent_start_margin:
             collapsible_with_parent_start_margin.0,
@@ -202,56 +199,52 @@ fn layout_block_level_children<'a>(
         current_margin: CollapsedMargin::zero(),
         current_block_direction_position: Length::zero(),
     };
-    let mut fragments: Vec<_>;
-    if float_context.is_some() || !layout_context.use_rayon {
-        // Because floats are involved, we do layout for this block formatting context
-        // in tree order without parallelism. This enables mutable access
-        // to a `FloatContext` that tracks every float encountered so far (again in tree order).
-        fragments = child_boxes
-            .iter()
-            .enumerate()
-            .map(|(tree_rank, box_)| {
-                let mut fragment = box_.layout(
-                    layout_context,
-                    containing_block,
-                    tree_rank,
-                    absolutely_positioned_fragments,
-                    float_context.as_mut().map(|c| &mut **c),
-                );
-                place_block_level_fragment(&mut fragment, &mut placement_state);
-                fragment
-            })
-            .collect()
-    } else {
-        fragments = child_boxes
-            .par_iter()
-            .enumerate()
-            .mapfold_reduce_into(
-                absolutely_positioned_fragments,
-                |abspos_fragments, (tree_rank, box_)| {
-                    box_.layout(
+    let fragments = positioning_context.adjust_static_positions(tree_rank, |positioning_context| {
+        if float_context.is_some() || !layout_context.use_rayon {
+            // Because floats are involved, we do layout for this block formatting context
+            // in tree order without parallelism. This enables mutable access
+            // to a `FloatContext` that tracks every float encountered so far (again in tree order).
+            child_boxes
+                .iter()
+                .enumerate()
+                .map(|(tree_rank, box_)| {
+                    let mut fragment = box_.layout(
                         layout_context,
+                        positioning_context,
                         containing_block,
                         tree_rank,
-                        abspos_fragments,
-                        /* float_context = */ None,
-                    )
-                },
-                |left_abspos_fragments, mut right_abspos_fragments| {
-                    left_abspos_fragments.append(&mut right_abspos_fragments);
-                },
-            )
-            .collect();
-        for fragment in &mut fragments {
-            place_block_level_fragment(fragment, &mut placement_state)
+                        float_context.as_mut().map(|c| &mut **c),
+                    );
+                    place_block_level_fragment(&mut fragment, &mut placement_state);
+                    fragment
+                })
+                .collect()
+        } else {
+            let has_positioned_ancestor = positioning_context.has_positioned_ancestor();
+            let mut fragments = child_boxes
+                .par_iter()
+                .enumerate()
+                .mapfold_reduce_into(
+                    positioning_context,
+                    |positioning_context, (tree_rank, box_)| {
+                        box_.layout(
+                            layout_context,
+                            positioning_context,
+                            containing_block,
+                            tree_rank,
+                            /* float_context = */ None,
+                        )
+                    },
+                    || PositioningContext::new_for_rayon(has_positioned_ancestor),
+                    PositioningContext::append,
+                )
+                .collect();
+            for fragment in &mut fragments {
+                place_block_level_fragment(fragment, &mut placement_state)
+            }
+            fragments
         }
-    }
-
-    adjust_static_positions(
-        &mut absolutely_positioned_fragments[abspos_so_far..],
-        &mut fragments,
-        tree_rank,
-    );
+    });
 
     FlowLayout {
         fragments,
@@ -269,65 +262,63 @@ impl BlockLevelBox {
     fn layout<'a>(
         &'a self,
         layout_context: &LayoutContext,
+        positioning_context: &mut PositioningContext<'a>,
         containing_block: &ContainingBlock,
         tree_rank: usize,
-        absolutely_positioned_fragments: &mut Vec<AbsolutelyPositionedFragment<'a>>,
         float_context: Option<&mut FloatContext>,
     ) -> Fragment {
         match self {
             BlockLevelBox::SameFormattingContextBlock { style, contents } => {
-                Fragment::Box(layout_in_flow_non_replaced_block_level(
+                Fragment::Box(positioning_context.for_maybe_position_relative(
                     layout_context,
                     containing_block,
-                    absolutely_positioned_fragments,
                     style,
-                    BlockLevelKind::SameFormattingContextBlock,
-                    |containing_block, nested_abspos, collapsible_with_parent_start_margin| {
-                        contents.layout(
+                    |positioning_context| {
+                        layout_in_flow_non_replaced_block_level(
                             layout_context,
+                            positioning_context,
                             containing_block,
+                            style,
+                            NonReplacedContents::SameFormattingContextBlock(contents),
                             tree_rank,
-                            nested_abspos,
                             float_context,
-                            collapsible_with_parent_start_margin,
                         )
                     },
                 ))
             },
-            BlockLevelBox::Independent(contents) => match contents.as_replaced() {
-                Ok(replaced) => Fragment::Box(layout_in_flow_replaced_block_level(
-                    containing_block,
-                    &contents.style,
-                    replaced,
-                )),
-                Err(non_replaced) => Fragment::Box(layout_in_flow_non_replaced_block_level(
+            BlockLevelBox::Independent(contents) => {
+                Fragment::Box(positioning_context.for_maybe_position_relative(
                     layout_context,
                     containing_block,
-                    absolutely_positioned_fragments,
                     &contents.style,
-                    BlockLevelKind::EstablishesAnIndependentFormattingContext,
-                    |containing_block, nested_abspos, _| {
-                        let independent_layout = non_replaced.layout(
+                    |positioning_context| match contents.as_replaced() {
+                        Ok(replaced) => layout_in_flow_replaced_block_level(
+                            containing_block,
+                            &contents.style,
+                            replaced,
+                        ),
+                        Err(non_replaced) => layout_in_flow_non_replaced_block_level(
                             layout_context,
+                            positioning_context,
                             containing_block,
+                            &contents.style,
+                            NonReplacedContents::EstablishesAnIndependentFormattingContext(
+                                non_replaced,
+                            ),
                             tree_rank,
-                            nested_abspos,
-                        );
-                        FlowLayout {
-                            fragments: independent_layout.fragments,
-                            content_block_size: independent_layout.content_block_size,
-                            collapsible_margins_in_children: CollapsedBlockMargins::zero(),
-                        }
+                            float_context,
+                        ),
                     },
-                )),
+                ))
             },
             BlockLevelBox::OutOfFlowAbsolutelyPositionedBox(box_) => {
-                absolutely_positioned_fragments.push(box_.layout(Vec2::zero(), tree_rank));
+                positioning_context.push(box_.layout(Vec2::zero(), tree_rank));
                 Fragment::Anonymous(AnonymousFragment::no_op(
                     containing_block.style.writing_mode,
                 ))
             },
             BlockLevelBox::OutOfFlowFloatBox(_box_) => {
+                // FIXME: call for_maybe_position_relative here
                 // TODO
                 Fragment::Anonymous(AnonymousFragment::no_op(
                     containing_block.style.writing_mode,
@@ -337,25 +328,21 @@ impl BlockLevelBox {
     }
 }
 
-#[derive(PartialEq)]
-enum BlockLevelKind {
-    SameFormattingContextBlock,
-    EstablishesAnIndependentFormattingContext,
+enum NonReplacedContents<'a> {
+    SameFormattingContextBlock(&'a BlockContainer),
+    EstablishesAnIndependentFormattingContext(NonReplacedIFC<'a>),
 }
 
 /// https://drafts.csswg.org/css2/visudet.html#blockwidth
 /// https://drafts.csswg.org/css2/visudet.html#normal-block
 fn layout_in_flow_non_replaced_block_level<'a>(
     layout_context: &LayoutContext,
+    positioning_context: &mut PositioningContext<'a>,
     containing_block: &ContainingBlock,
-    absolutely_positioned_fragments: &mut Vec<AbsolutelyPositionedFragment<'a>>,
     style: &Arc<ComputedValues>,
-    block_level_kind: BlockLevelKind,
-    layout_contents: impl FnOnce(
-        &ContainingBlock,
-        &mut Vec<AbsolutelyPositionedFragment<'a>>,
-        CollapsibleWithParentStartMargin,
-    ) -> FlowLayout,
+    block_level_kind: NonReplacedContents<'a>,
+    tree_rank: usize,
+    float_context: Option<&mut FloatContext>,
 ) -> BoxFragment {
     let cbis = containing_block.inline_size;
     let padding = style.padding().percentages_relative_to(cbis);
@@ -428,83 +415,81 @@ fn layout_in_flow_non_replaced_block_level<'a>(
         "Mixed writing modes are not supported yet"
     );
 
-    let this_start_margin_can_collapse_with_children = CollapsibleWithParentStartMargin(
-        block_level_kind == BlockLevelKind::SameFormattingContextBlock &&
-            pb.block_start == Length::zero(),
-    );
-    let this_end_margin_can_collapse_with_children = block_size == LengthOrAuto::Auto &&
-        min_box_size.block == Length::zero() &&
-        pb.block_end == Length::zero() &&
-        block_level_kind == BlockLevelKind::SameFormattingContextBlock;
-    let mut nested_abspos = vec![];
-    let mut flow_layout = layout_contents(
-        &containing_block_for_children,
-        if style.get_box().position == Position::Relative {
-            &mut nested_abspos
-        } else {
-            absolutely_positioned_fragments
-        },
-        this_start_margin_can_collapse_with_children,
-    );
     let mut block_margins_collapsed_with_children = CollapsedBlockMargins::from_margin(&margin);
-    if this_start_margin_can_collapse_with_children.0 {
-        block_margins_collapsed_with_children
-            .start
-            .adjoin_assign(&flow_layout.collapsible_margins_in_children.start);
-        if flow_layout
-            .collapsible_margins_in_children
-            .collapsed_through
-        {
-            block_margins_collapsed_with_children
-                .start
-                .adjoin_assign(&std::mem::replace(
-                    &mut flow_layout.collapsible_margins_in_children.end,
-                    CollapsedMargin::zero(),
-                ));
-        }
-    }
-    if this_end_margin_can_collapse_with_children {
-        block_margins_collapsed_with_children
-            .end
-            .adjoin_assign(&flow_layout.collapsible_margins_in_children.end);
-    } else {
-        flow_layout.content_block_size += flow_layout.collapsible_margins_in_children.end.solve();
-    }
-    block_margins_collapsed_with_children.collapsed_through =
-        this_start_margin_can_collapse_with_children.0 &&
-            this_end_margin_can_collapse_with_children &&
-            flow_layout
-                .collapsible_margins_in_children
-                .collapsed_through;
-    let relative_adjustement = relative_adjustement(style, inline_size, block_size);
+
+    let fragments;
+    let mut content_block_size;
+    match block_level_kind {
+        NonReplacedContents::SameFormattingContextBlock(contents) => {
+            let this_start_margin_can_collapse_with_children = pb.block_start == Length::zero();
+            let this_end_margin_can_collapse_with_children = pb.block_end == Length::zero() &&
+                block_size == LengthOrAuto::Auto &&
+                min_box_size.block == Length::zero();
+
+            let flow_layout = contents.layout(
+                layout_context,
+                positioning_context,
+                &containing_block_for_children,
+                tree_rank,
+                float_context,
+                CollapsibleWithParentStartMargin(this_start_margin_can_collapse_with_children),
+            );
+            fragments = flow_layout.fragments;
+            content_block_size = flow_layout.content_block_size;
+            let mut collapsible_margins_in_children = flow_layout.collapsible_margins_in_children;
+
+            if this_start_margin_can_collapse_with_children {
+                block_margins_collapsed_with_children
+                    .start
+                    .adjoin_assign(&collapsible_margins_in_children.start);
+                if collapsible_margins_in_children.collapsed_through {
+                    block_margins_collapsed_with_children
+                        .start
+                        .adjoin_assign(&std::mem::replace(
+                            &mut collapsible_margins_in_children.end,
+                            CollapsedMargin::zero(),
+                        ));
+                }
+            }
+            if this_end_margin_can_collapse_with_children {
+                block_margins_collapsed_with_children
+                    .end
+                    .adjoin_assign(&collapsible_margins_in_children.end);
+            } else {
+                content_block_size += collapsible_margins_in_children.end.solve();
+            }
+            block_margins_collapsed_with_children.collapsed_through =
+                this_start_margin_can_collapse_with_children &&
+                    this_end_margin_can_collapse_with_children &&
+                    collapsible_margins_in_children.collapsed_through;
+        },
+        NonReplacedContents::EstablishesAnIndependentFormattingContext(non_replaced) => {
+            let independent_layout = non_replaced.layout(
+                layout_context,
+                positioning_context,
+                &containing_block_for_children,
+                tree_rank,
+            );
+            fragments = independent_layout.fragments;
+            content_block_size = independent_layout.content_block_size;
+        },
+    };
     let block_size = block_size.auto_is(|| {
-        flow_layout
-            .content_block_size
-            .clamp_between_extremums(min_box_size.block, max_box_size.block)
+        content_block_size.clamp_between_extremums(min_box_size.block, max_box_size.block)
     });
     let content_rect = Rect {
         start_corner: Vec2 {
-            block: pb.block_start + relative_adjustement.block,
-            inline: pb.inline_start + relative_adjustement.inline + margin.inline_start,
+            block: pb.block_start,
+            inline: pb.inline_start,
         },
         size: Vec2 {
             block: block_size,
             inline: inline_size,
         },
     };
-    if style.get_box().position == Position::Relative {
-        AbsolutelyPositionedFragment::in_positioned_containing_block(
-            layout_context,
-            &nested_abspos,
-            &mut flow_layout.fragments,
-            &content_rect.size,
-            &padding,
-            style,
-        )
-    }
     BoxFragment {
         style: style.clone(),
-        children: flow_layout.fragments,
+        children: fragments,
         content_rect,
         padding,
         border,
@@ -543,15 +528,10 @@ fn layout_in_flow_replaced_block_level<'a>(
         block_end: computed_margin.block_end.auto_is(Length::zero),
     };
     let fragments = replaced.make_fragments(style, size.clone());
-    let relative_adjustement = relative_adjustement(
-        style,
-        size.inline,
-        LengthOrAuto::LengthPercentage(size.block),
-    );
     let content_rect = Rect {
         start_corner: Vec2 {
-            block: pb.block_start + relative_adjustement.block,
-            inline: pb.inline_start + relative_adjustement.inline + margin.inline_start,
+            block: pb.block_start,
+            inline: pb.inline_start + margin.inline_start,
         },
         size,
     };
diff --git a/components/layout_2020/flow/root.rs b/components/layout_2020/flow/root.rs
index 15dc6d404b6..24dea984e62 100644
--- a/components/layout_2020/flow/root.rs
+++ b/components/layout_2020/flow/root.rs
@@ -12,12 +12,12 @@ use crate::formatting_contexts::IndependentFormattingContext;
 use crate::fragments::Fragment;
 use crate::geom;
 use crate::geom::flow_relative::Vec2;
-use crate::positioned::{AbsolutelyPositionedBox, AbsolutelyPositionedFragment};
+use crate::positioned::AbsolutelyPositionedBox;
+use crate::positioned::PositioningContext;
 use crate::replaced::ReplacedContent;
 use crate::sizing::ContentSizesRequest;
 use crate::style_ext::{Display, DisplayGeneratingBox, DisplayInside};
 use crate::DefiniteContainingBlock;
-use rayon::iter::{IntoParallelRefIterator, ParallelExtend, ParallelIterator};
 use script_layout_interface::wrapper_traits::LayoutNode;
 use servo_arc::Arc;
 use style::properties::ComputedValues;
@@ -110,25 +110,19 @@ impl BoxTreeRoot {
         };
 
         let dummy_tree_rank = 0;
-        let mut absolutely_positioned_fragments = vec![];
+        let mut positioning_context = PositioningContext::new_for_initial_containing_block();
         let mut independent_layout = self.0.layout(
             layout_context,
+            &mut positioning_context,
             &(&initial_containing_block).into(),
             dummy_tree_rank,
-            &mut absolutely_positioned_fragments,
         );
 
-        let map =
-            |a: &AbsolutelyPositionedFragment| a.layout(layout_context, &initial_containing_block);
-        if layout_context.use_rayon {
-            independent_layout
-                .fragments
-                .par_extend(absolutely_positioned_fragments.par_iter().map(map))
-        } else {
-            independent_layout
-                .fragments
-                .extend(absolutely_positioned_fragments.iter().map(map))
-        }
+        positioning_context.layout_in_initial_containing_block(
+            layout_context,
+            &initial_containing_block,
+            &mut independent_layout.fragments,
+        );
 
         FragmentTreeRoot(independent_layout.fragments)
     }
diff --git a/components/layout_2020/formatting_contexts.rs b/components/layout_2020/formatting_contexts.rs
index eb90d62c926..dcbbfa370a6 100644
--- a/components/layout_2020/formatting_contexts.rs
+++ b/components/layout_2020/formatting_contexts.rs
@@ -6,7 +6,7 @@ use crate::context::LayoutContext;
 use crate::dom_traversal::{Contents, NodeExt};
 use crate::flow::BlockFormattingContext;
 use crate::fragments::Fragment;
-use crate::positioned::AbsolutelyPositionedFragment;
+use crate::positioned::PositioningContext;
 use crate::replaced::ReplacedContent;
 use crate::sizing::{BoxContentSizes, ContentSizesRequest};
 use crate::style_ext::DisplayInside;
@@ -101,16 +101,16 @@ impl<'a> NonReplacedIFC<'a> {
     pub fn layout(
         &self,
         layout_context: &LayoutContext,
+        positioning_context: &mut PositioningContext<'a>,
         containing_block: &ContainingBlock,
         tree_rank: usize,
-        absolutely_positioned_fragments: &mut Vec<AbsolutelyPositionedFragment<'a>>,
     ) -> IndependentLayout {
         match &self.0 {
             NonReplacedIFCKind::Flow(bfc) => bfc.layout(
                 layout_context,
+                positioning_context,
                 containing_block,
                 tree_rank,
-                absolutely_positioned_fragments,
             ),
         }
     }
diff --git a/components/layout_2020/lib.rs b/components/layout_2020/lib.rs
index 8e923f870d7..b8cc003caf5 100644
--- a/components/layout_2020/lib.rs
+++ b/components/layout_2020/lib.rs
@@ -27,11 +27,8 @@ pub mod wrapper;
 pub use flow::{BoxTreeRoot, FragmentTreeRoot};
 
 use crate::geom::flow_relative::Vec2;
-use crate::style_ext::ComputedValuesExt;
-use style::computed_values::position::T as Position;
 use style::properties::ComputedValues;
 use style::values::computed::{Length, LengthOrAuto};
-use style::Zero;
 
 struct ContainingBlock<'a> {
     inline_size: Length,
@@ -53,30 +50,3 @@ impl<'a> From<&'_ DefiniteContainingBlock<'a>> for ContainingBlock<'a> {
         }
     }
 }
-
-/// https://drafts.csswg.org/css2/visuren.html#relative-positioning
-fn relative_adjustement(
-    style: &ComputedValues,
-    inline_size: Length,
-    block_size: LengthOrAuto,
-) -> Vec2<Length> {
-    if style.get_box().position != Position::Relative {
-        return Vec2::zero();
-    }
-    fn adjust(start: LengthOrAuto, end: LengthOrAuto) -> Length {
-        match (start, end) {
-            (LengthOrAuto::Auto, LengthOrAuto::Auto) => Length::zero(),
-            (LengthOrAuto::Auto, LengthOrAuto::LengthPercentage(end)) => -end,
-            (LengthOrAuto::LengthPercentage(start), _) => start,
-        }
-    }
-    let block_size = block_size.auto_is(Length::zero);
-    let box_offsets = style.box_offsets().map_inline_and_block_axes(
-        |v| v.percentage_relative_to(inline_size),
-        |v| v.percentage_relative_to(block_size),
-    );
-    Vec2 {
-        inline: adjust(box_offsets.inline_start, box_offsets.inline_end),
-        block: adjust(box_offsets.block_start, box_offsets.block_end),
-    }
-}
diff --git a/components/layout_2020/positioned.rs b/components/layout_2020/positioned.rs
index b9c64ea54d3..cfe615ae27d 100644
--- a/components/layout_2020/positioned.rs
+++ b/components/layout_2020/positioned.rs
@@ -10,8 +10,10 @@ use crate::geom::flow_relative::{Rect, Sides, Vec2};
 use crate::sizing::ContentSizesRequest;
 use crate::style_ext::{ComputedValuesExt, DisplayInside};
 use crate::{ContainingBlock, DefiniteContainingBlock};
-use rayon::iter::{IntoParallelRefIterator, ParallelIterator};
+use rayon::iter::{IntoParallelRefIterator, ParallelExtend};
+use rayon_croissant::ParallelIteratorExt;
 use servo_arc::Arc;
+use style::computed_values::position::T as Position;
 use style::properties::ComputedValues;
 use style::values::computed::{Length, LengthOrAuto, LengthPercentage, LengthPercentageOrAuto};
 use style::Zero;
@@ -21,9 +23,14 @@ pub(crate) struct AbsolutelyPositionedBox {
     pub contents: IndependentFormattingContext,
 }
 
+pub(crate) struct PositioningContext<'box_tree> {
+    for_nearest_positioned_ancestor: Option<Vec<HoistedAbsolutelyPositionedBox<'box_tree>>>,
+    for_initial_containing_block: Vec<HoistedAbsolutelyPositionedBox<'box_tree>>,
+}
+
 #[derive(Debug)]
-pub(crate) struct AbsolutelyPositionedFragment<'box_> {
-    absolutely_positioned_box: &'box_ AbsolutelyPositionedBox,
+pub(crate) struct HoistedAbsolutelyPositionedBox<'box_tree> {
+    absolutely_positioned_box: &'box_tree AbsolutelyPositionedBox,
 
     /// The rank of the child from which this absolutely positioned fragment
     /// came from, when doing the layout of a block container. Used to compute
@@ -77,11 +84,11 @@ impl AbsolutelyPositionedBox {
         }
     }
 
-    pub(crate) fn layout<'a>(
-        &'a self,
+    pub(crate) fn layout(
+        &self,
         initial_start_corner: Vec2<Length>,
         tree_rank: usize,
-    ) -> AbsolutelyPositionedFragment {
+    ) -> HoistedAbsolutelyPositionedBox {
         fn absolute_box_offsets(
             initial_static_start: Length,
             start: LengthPercentageOrAuto,
@@ -98,7 +105,7 @@ impl AbsolutelyPositionedBox {
         }
 
         let box_offsets = self.contents.style.box_offsets();
-        AbsolutelyPositionedFragment {
+        HoistedAbsolutelyPositionedBox {
             absolutely_positioned_box: self,
             tree_rank,
             box_offsets: Vec2 {
@@ -117,46 +124,217 @@ impl AbsolutelyPositionedBox {
     }
 }
 
-impl<'a> AbsolutelyPositionedFragment<'a> {
-    pub(crate) fn in_positioned_containing_block(
+impl<'box_tree> PositioningContext<'box_tree> {
+    pub(crate) fn new_for_initial_containing_block() -> Self {
+        Self {
+            for_nearest_positioned_ancestor: None,
+            for_initial_containing_block: Vec::new(),
+        }
+    }
+
+    pub(crate) fn new_for_rayon(has_positioned_ancestor: bool) -> Self {
+        Self {
+            for_nearest_positioned_ancestor: if has_positioned_ancestor {
+                Some(Vec::new())
+            } else {
+                None
+            },
+            for_initial_containing_block: Vec::new(),
+        }
+    }
+
+    pub(crate) fn has_positioned_ancestor(&self) -> bool {
+        self.for_nearest_positioned_ancestor.is_some()
+    }
+
+    pub(crate) fn for_maybe_position_relative(
+        &mut self,
         layout_context: &LayoutContext,
-        absolute: &[Self],
-        fragments: &mut Vec<Fragment>,
-        content_rect_size: &Vec2<Length>,
-        padding: &Sides<Length>,
+        containing_block: &ContainingBlock,
         style: &ComputedValues,
+        f: impl FnOnce(&mut Self) -> BoxFragment,
+    ) -> BoxFragment {
+        if style.clone_position() == Position::Relative {
+            let mut fragment =
+                // Establing a containing block for absolutely positioned descendants
+                Self::for_positioned(layout_context, &mut self.for_initial_containing_block, f);
+
+            fragment.content_rect.start_corner += &relative_adjustement(style, containing_block);
+            fragment
+        } else {
+            f(self)
+        }
+    }
+
+    fn for_positioned(
+        layout_context: &LayoutContext,
+        for_initial_containing_block: &mut Vec<HoistedAbsolutelyPositionedBox<'box_tree>>,
+        f: impl FnOnce(&mut Self) -> BoxFragment,
+    ) -> BoxFragment {
+        let mut new = Self {
+            for_nearest_positioned_ancestor: Some(Vec::new()),
+            for_initial_containing_block: std::mem::take(for_initial_containing_block),
+        };
+        let mut positioned_box_fragment = f(&mut new);
+        new.layout_in_positioned_ancestor(layout_context, &mut positioned_box_fragment);
+        *for_initial_containing_block = new.for_initial_containing_block;
+        positioned_box_fragment
+    }
+
+    pub(crate) fn push(&mut self, box_: HoistedAbsolutelyPositionedBox<'box_tree>) {
+        if let Some(nearest) = &mut self.for_nearest_positioned_ancestor {
+            match box_
+                .absolutely_positioned_box
+                .contents
+                .style
+                .clone_position()
+            {
+                Position::Fixed => {}, // fall through
+                Position::Absolute => return nearest.push(box_),
+                Position::Static | Position::Relative => unreachable!(),
+            }
+        }
+        self.for_initial_containing_block.push(box_)
+    }
+
+    pub(crate) fn append(&mut self, other: Self) {
+        vec_append_owned(
+            &mut self.for_initial_containing_block,
+            other.for_initial_containing_block,
+        );
+        match (
+            self.for_nearest_positioned_ancestor.as_mut(),
+            other.for_nearest_positioned_ancestor,
+        ) {
+            (Some(a), Some(b)) => vec_append_owned(a, b),
+            (None, None) => {},
+            _ => unreachable!(),
+        }
+    }
+
+    pub(crate) fn adjust_static_positions(
+        &mut self,
+        tree_rank_in_parent: usize,
+        f: impl FnOnce(&mut Self) -> Vec<Fragment>,
+    ) -> Vec<Fragment> {
+        let for_icb_so_far = self.for_initial_containing_block.len();
+        let for_nearest_so_far = self
+            .for_nearest_positioned_ancestor
+            .as_ref()
+            .map(|v| v.len());
+
+        let fragments = f(self);
+
+        adjust_static_positions(
+            &mut self.for_initial_containing_block[for_icb_so_far..],
+            &fragments,
+            tree_rank_in_parent,
+        );
+        if let Some(nearest) = &mut self.for_nearest_positioned_ancestor {
+            adjust_static_positions(
+                &mut nearest[for_nearest_so_far.unwrap()..],
+                &fragments,
+                tree_rank_in_parent,
+            );
+        }
+        fragments
+    }
+
+    pub(crate) fn layout_in_initial_containing_block(
+        &mut self,
+        layout_context: &LayoutContext,
+        initial_containing_block: &DefiniteContainingBlock,
+        fragments: &mut Vec<Fragment>,
     ) {
-        if absolute.is_empty() {
-            return;
+        debug_assert!(self.for_nearest_positioned_ancestor.is_none());
+
+        // Loop because it’s possible that we discover (the static position of)
+        // more absolutely-positioned boxes while doing layout for others.
+        while !self.for_initial_containing_block.is_empty() {
+            HoistedAbsolutelyPositionedBox::layout_many(
+                layout_context,
+                &std::mem::take(&mut self.for_initial_containing_block),
+                fragments,
+                &mut self.for_initial_containing_block,
+                initial_containing_block,
+            )
         }
-        let padding_rect = Rect {
-            size: content_rect_size.clone(),
-            // Ignore the content rect’s position in its own containing block:
-            start_corner: Vec2::zero(),
+    }
+
+    fn layout_in_positioned_ancestor(
+        &mut self,
+        layout_context: &LayoutContext,
+        positioned_box_fragment: &mut BoxFragment,
+    ) {
+        let for_here = self.for_nearest_positioned_ancestor.take().unwrap();
+        if !for_here.is_empty() {
+            let padding_rect = Rect {
+                size: positioned_box_fragment.content_rect.size.clone(),
+                // Ignore the content rect’s position in its own containing block:
+                start_corner: Vec2::zero(),
+            }
+            .inflate(&positioned_box_fragment.padding);
+            let containing_block = DefiniteContainingBlock {
+                size: padding_rect.size.clone(),
+                style: &positioned_box_fragment.style,
+            };
+            let mut children = Vec::new();
+            HoistedAbsolutelyPositionedBox::layout_many(
+                layout_context,
+                &for_here,
+                &mut children,
+                &mut self.for_initial_containing_block,
+                &containing_block,
+            );
+            positioned_box_fragment
+                .children
+                .push(Fragment::Anonymous(AnonymousFragment {
+                    children,
+                    rect: padding_rect,
+                    mode: positioned_box_fragment.style.writing_mode,
+                }))
         }
-        .inflate(&padding);
-        let containing_block = DefiniteContainingBlock {
-            size: padding_rect.size.clone(),
-            style,
-        };
-        let map = |a: &AbsolutelyPositionedFragment| a.layout(layout_context, &containing_block);
-        let children = if layout_context.use_rayon {
-            absolute.par_iter().map(map).collect()
+    }
+}
+
+impl<'box_tree> HoistedAbsolutelyPositionedBox<'box_tree> {
+    pub(crate) fn layout_many(
+        layout_context: &LayoutContext,
+        boxes: &[Self],
+        fragments: &mut Vec<Fragment>,
+        for_initial_containing_block: &mut Vec<HoistedAbsolutelyPositionedBox<'box_tree>>,
+        containing_block: &DefiniteContainingBlock,
+    ) {
+        if layout_context.use_rayon {
+            fragments.par_extend(boxes.par_iter().mapfold_reduce_into(
+                for_initial_containing_block,
+                |for_initial_containing_block, box_| {
+                    Fragment::Box(box_.layout(
+                        layout_context,
+                        for_initial_containing_block,
+                        containing_block,
+                    ))
+                },
+                Vec::new,
+                vec_append_owned,
+            ))
         } else {
-            absolute.iter().map(map).collect()
-        };
-        fragments.push(Fragment::Anonymous(AnonymousFragment {
-            children,
-            rect: padding_rect,
-            mode: style.writing_mode,
-        }))
+            fragments.extend(boxes.iter().map(|box_| {
+                Fragment::Box(box_.layout(
+                    layout_context,
+                    for_initial_containing_block,
+                    containing_block,
+                ))
+            }))
+        }
     }
 
     pub(crate) fn layout(
         &self,
         layout_context: &LayoutContext,
+        for_initial_containing_block: &mut Vec<HoistedAbsolutelyPositionedBox<'box_tree>>,
         containing_block: &DefiniteContainingBlock,
-    ) -> Fragment {
+    ) -> BoxFragment {
         let style = &self.absolutely_positioned_box.contents.style;
         let cbis = containing_block.size.inline;
         let cbbs = containing_block.size.block;
@@ -216,95 +394,89 @@ impl<'a> AbsolutelyPositionedFragment<'a> {
             block_end: block_axis.margin_end,
         };
 
-        let mut absolutely_positioned_fragments = Vec::new();
-        let (size, mut fragments) = match self.absolutely_positioned_box.contents.as_replaced() {
-            Ok(replaced) => {
-                // https://drafts.csswg.org/css2/visudet.html#abs-replaced-width
-                // https://drafts.csswg.org/css2/visudet.html#abs-replaced-height
-                let style = &self.absolutely_positioned_box.contents.style;
-                let size = replaced_used_size.unwrap();
-                let fragments = replaced.make_fragments(style, size.clone());
-                (size, fragments)
-            },
-            Err(non_replaced) => {
-                // https://drafts.csswg.org/css2/visudet.html#abs-non-replaced-width
-                // https://drafts.csswg.org/css2/visudet.html#abs-non-replaced-height
-                let inline_size = inline_axis.size.auto_is(|| {
-                    let available_size = match inline_axis.anchor {
-                        Anchor::Start(start) => {
-                            cbis - start - pb.inline_sum() - margin.inline_sum()
-                        },
-                        Anchor::End(end) => cbis - end - pb.inline_sum() - margin.inline_sum(),
+        let for_icb = for_initial_containing_block;
+        PositioningContext::for_positioned(layout_context, for_icb, |positioning_context| {
+            let size;
+            let fragments;
+            match self.absolutely_positioned_box.contents.as_replaced() {
+                Ok(replaced) => {
+                    // https://drafts.csswg.org/css2/visudet.html#abs-replaced-width
+                    // https://drafts.csswg.org/css2/visudet.html#abs-replaced-height
+                    let style = &self.absolutely_positioned_box.contents.style;
+                    size = replaced_used_size.unwrap();
+                    fragments = replaced.make_fragments(style, size.clone());
+                },
+                Err(non_replaced) => {
+                    // https://drafts.csswg.org/css2/visudet.html#abs-non-replaced-width
+                    // https://drafts.csswg.org/css2/visudet.html#abs-non-replaced-height
+                    let inline_size = inline_axis.size.auto_is(|| {
+                        let available_size = match inline_axis.anchor {
+                            Anchor::Start(start) => {
+                                cbis - start - pb.inline_sum() - margin.inline_sum()
+                            },
+                            Anchor::End(end) => cbis - end - pb.inline_sum() - margin.inline_sum(),
+                        };
+                        self.absolutely_positioned_box
+                            .contents
+                            .content_sizes
+                            .shrink_to_fit(available_size)
+                    });
+
+                    let containing_block_for_children = ContainingBlock {
+                        inline_size,
+                        block_size: block_axis.size,
+                        style,
                     };
-                    self.absolutely_positioned_box
-                        .contents
-                        .content_sizes
-                        .shrink_to_fit(available_size)
-                });
-
-                let containing_block_for_children = ContainingBlock {
-                    inline_size,
-                    block_size: block_axis.size,
-                    style,
-                };
-                // https://drafts.csswg.org/css-writing-modes/#orthogonal-flows
-                assert_eq!(
-                    containing_block.style.writing_mode,
-                    containing_block_for_children.style.writing_mode,
-                    "Mixed writing modes are not supported yet"
-                );
-                let dummy_tree_rank = 0;
-                let independent_layout = non_replaced.layout(
-                    layout_context,
-                    &containing_block_for_children,
-                    dummy_tree_rank,
-                    &mut absolutely_positioned_fragments,
-                );
-
-                let size = Vec2 {
-                    inline: inline_size,
-                    block: block_axis
-                        .size
-                        .auto_is(|| independent_layout.content_block_size),
-                };
-                (size, independent_layout.fragments)
-            },
-        };
+                    // https://drafts.csswg.org/css-writing-modes/#orthogonal-flows
+                    assert_eq!(
+                        containing_block.style.writing_mode,
+                        containing_block_for_children.style.writing_mode,
+                        "Mixed writing modes are not supported yet"
+                    );
+                    let dummy_tree_rank = 0;
+                    let independent_layout = non_replaced.layout(
+                        layout_context,
+                        positioning_context,
+                        &containing_block_for_children,
+                        dummy_tree_rank,
+                    );
 
-        let inline_start = match inline_axis.anchor {
-            Anchor::Start(start) => start + pb.inline_start + margin.inline_start,
-            Anchor::End(end) => cbbs - end - pb.inline_end - margin.inline_end - size.inline,
-        };
-        let block_start = match block_axis.anchor {
-            Anchor::Start(start) => start + pb.block_start + margin.block_start,
-            Anchor::End(end) => cbbs - end - pb.block_end - margin.block_end - size.block,
-        };
+                    size = Vec2 {
+                        inline: inline_size,
+                        block: block_axis
+                            .size
+                            .auto_is(|| independent_layout.content_block_size),
+                    };
+                    fragments = independent_layout.fragments
+                },
+            };
 
-        let content_rect = Rect {
-            start_corner: Vec2 {
-                inline: inline_start,
-                block: block_start,
-            },
-            size,
-        };
+            let inline_start = match inline_axis.anchor {
+                Anchor::Start(start) => start + pb.inline_start + margin.inline_start,
+                Anchor::End(end) => cbis - end - pb.inline_end - margin.inline_end - size.inline,
+            };
+            let block_start = match block_axis.anchor {
+                Anchor::Start(start) => start + pb.block_start + margin.block_start,
+                Anchor::End(end) => cbbs - end - pb.block_end - margin.block_end - size.block,
+            };
 
-        AbsolutelyPositionedFragment::in_positioned_containing_block(
-            layout_context,
-            &absolutely_positioned_fragments,
-            &mut fragments,
-            &content_rect.size,
-            &padding,
-            style,
-        );
+            let content_rect = Rect {
+                start_corner: Vec2 {
+                    inline: inline_start,
+                    block: block_start,
+                },
+                size,
+            };
 
-        Fragment::Box(BoxFragment {
-            style: style.clone(),
-            children: fragments,
-            content_rect,
-            padding,
-            border,
-            margin,
-            block_margins_collapsed_with_children: CollapsedBlockMargins::zero(),
+            BoxFragment {
+                style: style.clone(),
+                children: fragments,
+                content_rect,
+                padding,
+                border,
+                margin,
+                block_margins_collapsed_with_children: CollapsedBlockMargins::zero(),
+            }
         })
     }
 }
@@ -413,9 +585,9 @@ fn solve_axis(
     }
 }
 
-pub(crate) fn adjust_static_positions(
-    absolutely_positioned_fragments: &mut [AbsolutelyPositionedFragment],
-    child_fragments: &mut [Fragment],
+fn adjust_static_positions(
+    absolutely_positioned_fragments: &mut [HoistedAbsolutelyPositionedBox],
+    child_fragments: &[Fragment],
     tree_rank_in_parent: usize,
 ) {
     for abspos_fragment in absolutely_positioned_fragments {
@@ -436,3 +608,35 @@ pub(crate) fn adjust_static_positions(
         }
     }
 }
+
+fn vec_append_owned<T>(a: &mut Vec<T>, mut b: Vec<T>) {
+    if a.is_empty() {
+        *a = b
+    } else {
+        a.append(&mut b)
+    }
+}
+
+/// https://drafts.csswg.org/css2/visuren.html#relative-positioning
+pub(crate) fn relative_adjustement(
+    style: &ComputedValues,
+    containing_block: &ContainingBlock,
+) -> Vec2<Length> {
+    let cbis = containing_block.inline_size;
+    let cbbs = containing_block.block_size.auto_is(Length::zero);
+    let box_offsets = style.box_offsets().map_inline_and_block_axes(
+        |v| v.percentage_relative_to(cbis),
+        |v| v.percentage_relative_to(cbbs),
+    );
+    fn adjust(start: LengthOrAuto, end: LengthOrAuto) -> Length {
+        match (start, end) {
+            (LengthOrAuto::Auto, LengthOrAuto::Auto) => Length::zero(),
+            (LengthOrAuto::Auto, LengthOrAuto::LengthPercentage(end)) => -end,
+            (LengthOrAuto::LengthPercentage(start), _) => start,
+        }
+    }
+    Vec2 {
+        inline: adjust(box_offsets.inline_start, box_offsets.inline_end),
+        block: adjust(box_offsets.block_start, box_offsets.block_end),
+    }
+}
diff --git a/components/style/properties/longhands/box.mako.rs b/components/style/properties/longhands/box.mako.rs
index b8b6cbc8c34..aa6118b8a8a 100644
--- a/components/style/properties/longhands/box.mako.rs
+++ b/components/style/properties/longhands/box.mako.rs
@@ -55,6 +55,9 @@ impl computed_value::T {
     pub fn is_absolutely_positioned(self) -> bool {
         matches!(self, Self::Absolute | Self::Fixed)
     }
+    pub fn is_relative(self) -> bool {
+        self == Self::Relative
+    }
 }
 </%helpers:single_keyword>
 
diff --git a/components/style/properties/shorthands/background.mako.rs b/components/style/properties/shorthands/background.mako.rs
index 011ff5cb3d8..124d4fe406c 100644
--- a/components/style/properties/shorthands/background.mako.rs
+++ b/components/style/properties/shorthands/background.mako.rs
@@ -193,6 +193,29 @@
     }
 </%helpers:shorthand>
 
+<%helpers:shorthand name="background"
+                    engines="servo-2020"
+                    sub_properties="background-color"
+                    spec="https://drafts.csswg.org/css-backgrounds/#the-background">
+    use crate::values::specified::Color;
+    use crate::parser::Parse;
+
+    pub fn parse_value<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Longhands, ParseError<'i>> {
+        Ok(expanded! {
+            background_color: Color::parse(context, input)?
+        })
+    }
+
+    impl<'a> ToCss for LonghandsToSerialize<'a>  {
+        fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result where W: fmt::Write {
+            self.background_color.to_css(dest)
+        }
+    }
+</%helpers:shorthand>
+
 <%helpers:shorthand name="background-position"
                     engines="gecko servo-2013"
                     flags="SHORTHAND_IN_GETCS"
diff --git a/tests/wpt/metadata-layout-2020/css/CSS2/box-display/block-in-inline-008.xht.ini b/tests/wpt/metadata-layout-2020/css/CSS2/box-display/block-in-inline-008.xht.ini
deleted file mode 100644
index 5089f96e696..00000000000
--- a/tests/wpt/metadata-layout-2020/css/CSS2/box-display/block-in-inline-008.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[block-in-inline-008.xht]
-  expected: FAIL
diff --git a/tests/wpt/metadata-layout-2020/css/CSS2/box-display/block-in-inline-relpos-001.xht.ini b/tests/wpt/metadata-layout-2020/css/CSS2/box-display/block-in-inline-relpos-001.xht.ini
deleted file mode 100644
index 36bc0e014bb..00000000000
--- a/tests/wpt/metadata-layout-2020/css/CSS2/box-display/block-in-inline-relpos-001.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[block-in-inline-relpos-001.xht]
-  expected: FAIL
diff --git a/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-001.xht.ini b/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-001.xht.ini
deleted file mode 100644
index fe9734b830b..00000000000
--- a/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-001.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[containing-block-001.xht]
-  expected: FAIL
diff --git a/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-002.xht.ini b/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-002.xht.ini
deleted file mode 100644
index e2c7dd3545b..00000000000
--- a/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-002.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[containing-block-002.xht]
-  expected: FAIL
diff --git a/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-003.xht.ini b/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-003.xht.ini
deleted file mode 100644
index 245262f0b90..00000000000
--- a/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-003.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[containing-block-003.xht]
-  expected: FAIL
diff --git a/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-004.xht.ini b/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-004.xht.ini
deleted file mode 100644
index 199c0c4dd37..00000000000
--- a/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-004.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[containing-block-004.xht]
-  expected: FAIL
diff --git a/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-005.xht.ini b/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-005.xht.ini
deleted file mode 100644
index 612786df8b4..00000000000
--- a/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-005.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[containing-block-005.xht]
-  expected: FAIL
diff --git a/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-006.xht.ini b/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-006.xht.ini
deleted file mode 100644
index 0394efb0d59..00000000000
--- a/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-006.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[containing-block-006.xht]
-  expected: FAIL
diff --git a/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-007.xht.ini b/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-007.xht.ini
deleted file mode 100644
index 0c000bb2cd3..00000000000
--- a/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-007.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[containing-block-007.xht]
-  expected: FAIL
diff --git a/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-008.xht.ini b/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-008.xht.ini
deleted file mode 100644
index dd630be0f54..00000000000
--- a/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-008.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[containing-block-008.xht]
-  expected: FAIL
diff --git a/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-010.xht.ini b/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-010.xht.ini
deleted file mode 100644
index af40eef0a5d..00000000000
--- a/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-010.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[containing-block-010.xht]
-  expected: FAIL
diff --git a/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-023.xht.ini b/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-023.xht.ini
new file mode 100644
index 00000000000..906c33cc7ca
--- /dev/null
+++ b/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-023.xht.ini
@@ -0,0 +1,2 @@
+[containing-block-023.xht]
+  expected: FAIL
diff --git a/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-026.xht.ini b/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-026.xht.ini
deleted file mode 100644
index 46f865284ca..00000000000
--- a/tests/wpt/metadata-layout-2020/css/CSS2/box-display/containing-block-026.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[containing-block-026.xht]
-  expected: FAIL