CSS and HTML are essentially configuration languages while critical are finite. JS is a scripting language its more complex. I get what your saying but i’ve run web dev teams since the late 90’s at an enterprise level for some of the worlds biggest brands. I have hired CSS and HTML only devs, its a pain as its hard to choreograph resources around the fact their skills don’t fill the entire frontend gap. Also, I would say the vast majority fenders of with mid level experience have JS skills. I also don’t believe specialising in CSS, HTML or JS placates you from being good at all of them. Many I have worked with are. I would heartily recommend learning as much as you can about everything, it makes you more employable and if nothing else it make your results are more satisfying. When I’m recruiting I’m looking primarily for passion, resourcefulness and adaptability. Implicit with in that in breadth.