Once the CSS has been prepared and sent to the client, there's nothing left for Drupal to get involved with, that's why such questions are off topic here.
CSS is a universal Language (sort of) and what applies to the markup produced by a Drupal site applies equally to the markup produced by any other method. There's nothing Drupal-specific about questions like these:
- How do I make x look like y with CSS?
- How do I find which CSS class or ID to target?
Those, and similar CSS-related questions, can be solved by learning the language and how to use browser dev tools to your advantage. Obviously those are not Drupal disciplines so covering them here would be going against the purpose of the site.
Stack Overflow is the right place to ask CSS questions, but you must remember that Stack Exchange sites are designed to be repositories of knowledge, not personal support forums. You mention that you've been asked Could you not simplify this?, and that's kind of the point....
An SE site is not somewhere you can post a link to your site, or an entire web page of styles let's say, and expect someone to dig through them all to find out what your issue is. It's too broad, there's too much room for ambiguity, and it simply doesn't make a good question for a Q+A site.
What you need to do is break the problem down into its smallest parts, and produce a small, self-contained example that demonstrates the issue. Don't get me wrong, this is a skill in and of itself, and one that takes a while to learn, but it's necessary to ask good programming questions (and those in closely related genres).
I'll try to address your individual questions as well:
So how to deal with kinds of questions without getting voted down here
Ask well researched, clear, on-topic questions in such a way that can be useful to future visitors of the site. This excludes questions about CSS/HTML syntax or general CSS/HTML development as already mentioned.
Is there are a anothere place where this should go?
As already mentioned the right place in the SE network is Stack Overflow. Beyond that I don't know where you'd ask about CSS, I tend not to stray too far from these walls for such help.
Should people voted the question up?
Not really possible to answer that, but if you want to look at it logically, then questions about CSS, which are off topic, should probably not be voted up, no.
Should I asked a moderator if the question is voted down?
Moderators have no say in how people use their votes so please don't raise flags for us to look into them, unless you suspect that one or more users are consistently targeting you with downvotes in a malicious manner.
Above all, read through the literature in the Help Center, that will give you a fuller idea of what this site is about, and the best way to use it. And, of course, raise individual concerns like this on the meta site, not on the main site itself.