Web developers,

What existing CSS do you struggle with most?

Can you think of an older feature from CSS2/ CSS3, that has been in all browsers for a long time, but still doesn't work the same cross-browser. And so you fight with it, you have to use a hack or workaround. Or you just cannot use that feature at all. Perhaps you haven't even thought about it in a long time because you wrote it off as unusable long ago.

Is there anything that still falls into that category?
What do you want fixed?

@jensimmons A CSS Feature I have longed for is a complete implementation of the `attr(name type)` in CSS properties other than `content`.

Usually, I just want to set colors, percents, or background or mask image URLs.

Example: changing / animating the background color on a <meter> depending on the `value` attribute required I make 20+ rules to roughly parse the value attribute, when with attr could have done it one rule.

Reference: https://drafts.csswg.org/css-values-5/#funcdef-attr

CSS Values and Units Module Level 5