Need start-up aid regarding bootstrap theme

Hey all!
So I installed the Core+Admin-Plugins and everything works great. Than I installed the bootstrap-theme, enabled it and everything looks bad now. So I thougt when I would downloaded a theme it would just look like like on the demo page. I know this is a really stupid question/topic but which steps are neccessary here to get this thing started?

This is how it looks like:
Unbena123nnt

Here is a screenshot from the demo page:
https://raw.githubusercontent.com/getgrav/grav-theme-bootstrap/develop/assets/readme_1.png

Again I know this is stupid but I'm also not a professional webdeveloper so please forgive me here!

I tried to copy the pages from the antimatter blog skeleton into my project and it also doesn't load the styles. Please see in the attached picture. Thank you!

Antimatter_theme_try

You also need to install the bootstrapper plugin:
http://getgrav.org/downloads/plugins
https://github.com/getgrav/grav-plugin-bootstrapper/zipball/1.3.0

I was, in fact, just reminded of this myself today :-)

Wow.. this is a way more complex than I thougt it would be to get this theme up and running. Thank you Paul!