Changing a post’s background colour?

I’ve been staring at all of the docs and done a lot of searching, but can’t seem to find what I’m looking for! I know the answer must be simple but I just can’t see it!

I just wondered how I change the background colour of a post?

I wanted to change the background colour for a whole category, so that every time I post to that category it comes up with a slightly different background and stands out, but this really isn’t all that necessary if there’s a simple solution that I can pop into my actual post at the time.

Any help would be brilliant

Ilione
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