Extract all colors into CSS variables
Extract all the colors in the stylesheet into CSS variables. This not only makes the colors easier to maintain, it also opens the door for having different color themes / schemes based on the same UI.
The variables should be named by function. If several functions share the same color, then those colors can be further extracted into color name variables. The color name variables should not be referenced directly in the CSS rules. Instead, they should only be referenced by the semantic variable names.