When I first started doing CSS, I quickly realised that it was full of limitations and so generated it with php, working around browser bugs, switching color scheme values with replaceable %%tokens%%, sending values with includes, modularizing repetative code and so on.
Over the years the init has picked up a few capabilities, simple mathematical expressions, minification and more, and has become a fairly powerful CSS "pre-processor" (a term that didn't even exist when I first started doing this back in 2004!). This is the gubbins of it right here.
One day I will make a proper wab page for this stuff, I swear! Until then, curious browsers can enjoy my own client notes (the "about this folder.txt" files), a few examples of my css "sheets" as well as some of their comprising modules and snippets. Note: all these examples have real, live corresponding versions in https://corz.org/inc/css/.