They use a “Content” template, that then is used for this About section.

Yeah, but when I use this template on my wiki, it doesn't work

Did you copy the code from the template into your wiki?

Can you share the page where you try it?

https://gearworks-fan.fandom.com/wiki/Testpage

I think i need additional CSS for correct work

Nvm

(error from my side)

The Content template uses 3 css classes:

<div class="content-header">
<div class="content-header__title">{{{Header|}}}</div>
<div class="content-header__body">{{{Body|}}}</div>
</div>

They use a kinda confusing system of several css files, both Common.css and Fandomdesktop.css and a few more imported css files, so it isn't that easy to find out.

The classes are (mostly) defined in Fandomdesktop.css, while a part of .content-header is also defined in Article.css (which is loaded before Fandomdesktop), of which some of it (.border-radius) is overwritten by Fandomdesktop.

I shake your hand ❤️