CSS for articles

Question

I am not sure if this forum is for asking questions, but I will try.

I am not a CSS expert. I assume that CSS can help format the articles. As far as I can tell, we cannot create CSS for articles we write; that is, we do not have access to the style tag. If there is a way to put CSS or an equivalent into articles, then I have not seen it and I look at the articles every day.

I tried looking at the CSS that is available to articles and there is a long list of styles but most of them seem to be for the page that articles are in but not the articles themselves. If I know more about CSS, then can I determine what CSS is available for auhors for use in articles? If not, then is there some documentation someplace of that? If not, then I think it would help to have that.