On AO3, that's true; their interface strips all CSS before you post. Which is a little bit aggravating, actually. I've filed a bug about it, although I can see why they do it.

but on dreamwidth, you can use your own CSS. Even if you don't use your own CSS to write an entire style, you can embed CSS in something else you say. For example, I'm styling the following paragraph:



Code looks like:

<div style="margin-left:2em;margin-right:2em;font-family:cursive;font-style:italic;color:blue;">This is an overly styled paragraph!</div>

You can do that around anything you post in dreamwidth,so if something is a blockquote but you don't like the blockquote style by default, you can use your own style. If you reuse the style frequently, you can write a little style sheet of your own to embed. I'm not sure if you can embed it in your journal style without a paid account,but you can certainly embed it manually at the top of each post.Getting into the technical details of how to do that is a little bit complicated unless you are sure it's something you want to try, but you absolutely can do it.