JavaScript and CSS stink in a lot of ways. CSS is pretty messy if you want to do something slightly weird or complicated, which is a large part of why we have frameworks for grids instead of just being able to write one. It seems you have to do this weird "margin: 0 auto" trick to center things sometimes. Last I heard, the only way to get something vertically centered is to make it a table cell and use "vertical-align: center" or something like that. A lot of the interesting CSS properties are inconsistently supported and/or have vendor prefixes; can you use border-radius yet and expect it to work in the big three browsers? If you want a page that fits in the window with a fixed footer, you have to use JS hacks to make it work (actually I don't think I ever got it right). Just the other day a friend of mine had to do some weird hack where he detected the width of the window and set CSS accordingly to make things work right on mobile devices. Honestly, browser inconsistency is half the problem.

As for JS itself, I'll just defer to Douglas Crockford and the infamous wat talk: https://www.destroyallsoftware.com/talks/wat .

If you want more, the HTML and SVG DOMs are not properly integrated. It turns out to be nearly impossible to have a functioning textarea inside SVG, or indeed any form of wrapped text. God knows I tried with Chrome and Firefox, and apparently it just gets worse with IE. I'm sure I'll encounter more irritants as I go on, or maybe someone else can chime in with something specific they encountered this week. Probably the reason you don't hear more specifics is that most of the irritations fade into the background as you work around them, leaving only a vague dissatisfaction.

Now granted, this is all much better than nothing. I know the web has enabled all kinds of cool things, which is the only reason anyone bothers to develop it. But I think it's absurd to call front-end dev a "solved problem", at least in any sense meant to silence pointing out potential improvements.