forum & respawn theme

So … I wanted to install the same forum on your website as you used in the demo version on this page “https://skywarriorthemes.com/respawn/forums/” … it looks good / simple and the style fits perfectly on the web.

So I downloaded the appropriate plugin, installed it, activated it.
The forum works great and the style of the forum, unlike yours, is a kind of runaway / unshaped / twisted, see the picture

PS: Screenshot

The green marking shows what it should look like according to your DEMO.
The blue markings are some weird and I would need a fix there

What could be the cause?