CSS is completely dependent on HTML. If you write poor HTML - then you've already shot yourself in the foot. If you can't learn them together - then it's really hard. People don't learn the different display types / or positioning, and then they freak out when they can't figure out why a margin-top isn't working on their inline element. I've never met anyone I consider to write decent markup or styles in any of my jobs. This is pretty good: https://maintainablecss.com/chapters/introduction/ - but it doesn't teach you CSS. It teaches you how to write maintainable CSS. MDN is the best we've got (so far)