I'm not a native speaker and maybe overstress my understanding of "being hard", but CSS and especially HTML are famous for their simplicity. One can start basic markupped text with a basic text editor in minutes. Of course any advanced features require some learning. But I don't like people calling basic web publishing technologies (which are decades old) to be "hard". Because they are designed to be simple and that'…
I would say that HTML and CSS is not hard, but complex. It's not the same thing. If something is hard, then the learning curve is very shallow but if it's complex then you can gain solid knowledge bit by bit.
So "html & css is complex" would be a better fitting title.