https://drafts.csswg.org/css-pseudo-4/#highlight-styling

[ISSUE 1] Are there any other properties that should be included here?

Should custom properties be allowed on highlight pseudos? What about use of cascading variables? If so, does the rule stating that non-inherited properties are to be treated as inherited, apply to registered custom properties where inherit = false?

I suppose these features are ok, given that we’ve completely isolated highlight inheritance from originating element inheritance. As a result, defining or changing a custom property value should already be unable to “escape” and affect layout.