QWOP, if you haven’t played it, is a ridiculous running game. Instead of pressing, say, the right arrow key to run, you must control each of the runner’s muscles independently. Pressing the keys Q, W, O, and P will each extend one leg or bend one knee. Coordinating them all is incredibly difficult, and you are usually lucky if you can make a full stride before falling on your head.
This is also how a lot of developers treat CSS. Instead of thinking about constructing a robust system, they focus on only one specific part of the desired result. Instead of asking, “How do I run?”, they ask, “How do I flex my knee?” I can teach you how to flex your knee, but if QWOP shows us anything, that knowledge might actually make running more difficult.
Trust CSS; it does good things for you if you let it. Learn how to solve for system behaviors. Unless you like running by pressing Q, W, O, and P.