Auto merge of #19255 - mstange:bug1417709, r=emilio

Bug 1417709 - Add -moz-appearance: -moz-mac-vibrant-titlebar-light/dark and system colors with the same name.

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These are the servo changes that need to go with [bug 1417709](https://bugzilla.mozilla.org/show_bug.cgi?id=1417709).

r? emilio

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- [ ] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

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