[Arkarr]

No way we could make / get a new CSS for the forum ? Because I personnally spend (too much) time here, I would like to see something less "simple" as we have now .
Sooo.... is it possible or no way ?

[klippy]

You can write a Web Extension for browsers (all latest browsers should support them) that will change styles on the forum, or add new stuff to it.
However, there's no need for anything "less simple", as the simpler it is, the easier is it to browse through these forums and read them. Even if they added something similar, it would have to be purely optional.

[OvidiuS]

You can create custom style using web extension like Klippy said.
Actually I tried to make one and it's pretty simple. Here is the outcome
http://d.pr/i/1kvNq
I used stylebot and tampermonkey for chrome.

ps. If you spend more time, you could actually change whole style of forum.

[fysiks]

Don't fix it if it ain't broke.

[Arkarr]

I understand the answer, espacially the last one wich is clear and correct. Anyway, I'll do my own theme as you suggested, guys.