Frontloops is an html/css practical course that works like a subscription for handcrafted tasks. You get a design with prepared assets, build it and then get a working code for the same task as a reference + some additional hints which are worth paying attention to!

This tool is made for quick prototyping, mocking, and learning CSS via tinkering its properties. The editor is capable of generating valid and prefixed, when necessary, CSS, SASS, SCSS, and LESS code compatible with all browsers

CSSBattle is an online CSS Code Golfing battleground. Here, players from all around the world try to visually replicate "Targets" in smallest possible CSS code and battle it out to get to the top of the leaderboard. Are You Game?