Ironically, the site is made using tables for layout! Like, the really old technique where the left and right margins of the content are actually td's with a bunch of &nbsp's inside.

I'm really surprised that someone would make a site this way nowadays. It is a lot more work than necessary and the end results are not great (as you can see here).

PS: Running this in your console will get to a mostly workable state (not great, but better):

[...document.querySelectorAll('*')].map(e => {e.style.width = 'auto';})

Edit: I did my good deed of the day by opening a PR that modernizes the site's markup and CSS, fixing the issues too:

https://github.com/GaijinEntertainment/daScript/pull/70