Nice introduction into CSS color formats by Joshua Comeau. I learned about the upcoming lch():

LCH is a color format that aims to be perceptually uniform to humans. Two colors with an equivalent “lightness” value should feel equally light!

Looks great!

Also, TIL about that rgb(r g b / a) thing I’ve seen a few times:

For most of CSS’ existence, we specified RGB colors using a slightly different syntax.

This changed in CSS Colors level 4, which introduces a standardized notation used across newer color formats. rgba() isn't explicitly deprecated, but it's recommended to use the newer format (fortunately, browser support is excellent).