WPT details: Tests added for custom property queries under: http://wpt.fyi/css/css-contain/container-queries/at-container-style-parsing.html http://wpt.fyi/css/css-contain/container-queries/at-container-style-serialization.html http://wpt.fyi/css/css-contain/container-queries/custom-property-style-queries.html
Support style() container queries without a declaration value, only a property name, as a way of matching non-initial values. Previously you would have to do: not style(--my-property: initial) Now you can do: style(--my-property) to match any non-initial value.