* [css-ui] Test serialization: `-webkit-appearance`

* fixup! [css-ui] Test serialization: `-webkit-appearance`

Change API used to set style in order to actually test the internals
referenced by the test title.

* fixup! [css-ui] Test serialization: `-webkit-appearance`

Introduce tests for property reference

* fixup! [css-ui] Test serialization: `-webkit-appearance`

Remove duplicate assertion

* fixup! [css-ui] Test serialization: `-webkit-appearance`

Comprehensive tests for property references have been added since these
tests were written. Remove the excess assertions in order to improve the
focus of these tests.

* fixup! [css-ui] Test serialization: `-webkit-appearance`

Add equivalent tests for unprefixed `appearance` property

* fixup! [css-ui] Test serialization: `-webkit-appearance`