In my personal experience, you have to start at the source of the problem: universities.

I am a senior product designer and spend 90% of my time doing designs in Sketch, and 10% of my time occasionally supporting dev teams who don't have [the right] UI dev talent.

But my formal degree is in computer science.

My story is an odd one, because I'd always been fascinated with design, but figured it would be hard to make a career out of it, so I went into CS instead, always keeping up with design on the side for some beer money through college.

Throughout four years of instruction at one of the top universities in the country for computer science, I had ONE lone project where HTML/CSS came into play, and they didn't even really grade against it. Outside of my university's CS program, there is a separate department called "computer information technology" where students learn things like Photoshop and generic web development, but even there they don't really teach HTML/CSS.

I haven't done a comprehensive search, but my inkling is that it's simply not taught [at any sort of depth]. DOM positioning is really not that difficult of a concept, but "full-stack" developers still can't figure out the difference between absolute and relative positioning. In product design, this is unacceptable. Frameworks can only get you so far.

As far as hiring goes, there's a level of what I call "nitpixeling" that's required to perfectly translate mockups into code, so ideal candidates will be sticklers for design, but know the best techniques for translating it into code.

How do you find these people? I look at portfolios and try to find evidence of obscure CSS knowledge. Font-smoothing, transforms, CSS-based animation, flash-of-unstyled-text (FOUT) performance remedies, and out-of-the-ordinary layouts. I'm talking unconventional layouts that you don't find in a framework.

Call it highly specific, but to me, these are signs of a UI dev who not only knows what they're doing, but will search for solutions to make things look right.

Look for self-proclaimed "Web Developers" and dig into the source of their portfolio site and/or projects they've worked on. People who advertise themselves as "Front End Engineers" are usually just Angular/React/Polymer wizards, but only competent in HTML/CSS. You've gotta look for the evidence that it's more than just competence.