Rachel hooks us up with what the CSS Working Group is talking about:
Styling scrollbars. This would come with properties like scrollbar-width and scrollbar-color. The best we have right now is proprietary WebKit stuff.
Aspect ratios. I imagine the CSS portion of this journey will be best handled if it plays nicely with the HTML intrinsicsize stuff.
Matching without specificity.:where() is :matches() with no specificity, and :matches() may become :is().
Logical Properties shorthand. The team is discussing a shorthand syntax for Logical Properties and the possibility logical would be default over the current physical with a defined "mode" in the stylesheet.