This site uses the WonderCMS Bootstrap 5 theme by Joaquim Homrighausen. The theme is compatible with WonderCMS 3.4.x and above.
This theme does not contain the actual Bootstrap 5 files since I believe in modular design and resource distribution.
The WCMS-BS5-LOCAL plugin for WonderCMS plugin comes with Bootstrap 5.x and will serve Bootstrap 5.x files from your web server.
You can download the theme here: github.com/joho1968/wcms-bs5
You can find more information about WonderCMS here
It's like a global text block that can contain whatever you want :-)