How important is knowing CSS as a raw skill?
CSS is a core part of every website with a front-end, along with HTML and JavaScript.
Obviously my whole portfolio won't consist of just CSS, but rather a few projects that do showcase some raw CSS talent.
It's assumed that every website with a front-end you make uses CSS, so I wouldn't say there's much of a need to demonstrate that you know specifically CSS if you have already demonstrated that with entire websites already.
If you don't know CSS then you're not a front-end developer, unless you plan on making websites that look like this.
but with the abundance of CMS such as Wordpress, plus Bootstrap and other CSS frameworks, it seems that CSS as a skill gets overlooked
As I say, it's assumed that because you're a front end developer that you already know CSS to a good enough degree for your skill level.
WordPress exists to abstract away development for non-developers, if you don't know CSS but know WordPress then in my opinion you're a WordPress developer user, not a front-end developer.
TLDR: If you don't know CSS you can't call yourself a front-end web developer - CSS is used in every website.
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