Hey @clausuk23 ! The site theme is custom, and honestly a little hacked together, I'm not sure I'd recommend using it, but you're absolutely welcome to, I've open sourced it here: https://bitbucket.org/andyprobasco/nodebb-theme-themanadrain
Some of the design also comes from plugins and custom widgets, which I'm happy to talk about, but it could definitely be annoying to put it together.
However the theme is MOSTLY based on the existing 'Material' theme, which you can get here: https://github.com/pichalite/nodebb-theme-material. It looks like it was updated 3 months ago so it might be in better shape than mine anyway. I'm willing to bet that the Material theme will give you a lot of what you're looking for with a lot less work than setting up mine would be. Both my theme and the Material theme should be free to use so don't worry about that.
I'm happy to talk forum-admin'ing so if you have any other questions let me know.