We actually allow front-end HTML/CSS questions as per:
What do we do with HTML/CSS questions that are code-based but simple and focused on layout or implementing a design?
It needs to be focused and show the user has tried stuff just as it would if it's an Illustrator, Photoshop, InDesign, etc... question. But the consensus is to allow them.
We have two tags to help support this html and css.
Personally, I'd be inclined to allow more of these questions but then I've also been in favor of more questions from all sorts of topics I won't go into since it might muddle the discussion.
While we have the opportunity to get some new members from the ill-fated webdesign.stackexchange.com I think we should encourage these questions and those members.