[css-pseudo] Safari’s ::selection “wash” and UA tweaks to highlight colors · Issue #6853 · w3c/csswg-drafts (original) (raw)
Safari has a special approach to painting text ::selection, where it only paints a “wash” on top of the text being selected (see #6022 irc log, “blue wash”, “magic transluscent”). The way this is achieved is interesting: iff the author sets the ::selection background to a fully-opaque color, Safari overrides the alpha value to make the color translucent (demo).
UA cannot do these weird things when the author has specified colors. They have to use the author-specified colors with no modification. But when using UA-chosen colors, they can choose anything.
I don’t think we can allow Safari to paint ::selection as a translucent “wash” and forbid Safari from making opaque ::selection backgrounds translucent, because any author unaware of Safari’s different approach might set the ::selection background to an opaque color (such as a named color or other color without alpha) while expecting the selected text to stay legible.
I want to agree with @fantasai here and forbid all UA tweaks to author highlight colors (see also #6150). But I think I’m biased here, because I also feel like we should forbid the “text wash”, because both of these would make it easier to specify and test highlight painting precisely.