Someone asked me this recently, and further explained themselves:
I have a WordPress template that I’m using and I want to completely re-design a couple of pages (visual changes only). I can create the front-end layouts, but I’m interested in learning about how complex/lengthy the process can be to implement said front-end layout, or if it’s a fairly minimal task.
Here’s what I said back: It depends on how familiar with frameworks where the front-end is generated on the server-side (HAML with Ruby, say, as another example.) WordPress uses PHP based server-side rendering – so when you go look at the code for a theme, you’ll see HTML interspersed with PHP, on top of which you’ll see (PHP) calls to the WordPress API.
If all of that is easy-peasy, then “re-designing” won’t be that hard, esp as you already know HTML/CSS.
It’s not that hard even if your experience is in “handle-bar style” frameworks like Angular. You still have to map things a bit into the hook/callback based setup you’ll see in WordPress but the learning curve is not that rough.