Styling of post delimiters in two different blogs

And submitted later …
Is it also possible to style the font sizes of text and headings, colors etc. separately for each category / post list?

thanks
Grobi

Hi Rkard,
of course I can drop a screenshot for a better explanation – this imgur-url may help. Hopefully it works:

<script async src=”//s.imgur.com/min/embed.js” charset=”utf-8″></script>

I have two columns, one 2/3-page-width and one 1/3. The blog-entries on the left side are displaying the category “Bericht” (report), the blog-entries in the column on the right side are showing the category “Wichtig & Aktuell” (important). In order to be able to visually distinguish both columns better, I have colored the right column background gray. But this styling is not enough. Out of consideration for the visitors to the site, it is important to me that you can see the dividing line between the entries. In my example, the light (almost white) delimiter in the left column can hardly be seen on the white background.
I would like to style it accordingly – but without automatically changing the dividing lines in the right column (or in the other category).

If this styling option were available – and further blog elements th change, too – that would be great.
Best Regards
Grobi