HOW TO:
Get some sort of custom CSS browser extension, I use "Stylus" on Brave (its on all chromium based browsers), and I believe it is also available on Firefox.
Point your custom CSS towards speedrun.com (duh) EDIT: If using the "Stylus" extension, select "URLs starting with" and put "https://www.speedrun.com"
Put in the CSS from here: https://hatebin.com/hhhclkygus ( credits @SioN ) or put in the CSS from here: https://hatebin.com/dpfqwkoums ( credits @1UpsForLife )
It works for me, if it doesn't work for anyone else please reply here so I can try to find a fix.
EDIT: @dha had a bug where the leaderboard was moved to the bottom of the screen. Apparently if this happens you want to make sure you set your browsers zoom to 100%
Doesn't seem remove the side margin on game/run pages. Even manually ripping out HTML with Inspect Element I can't figure out how to get rid of that.
@ShikenNuggets I see what you mean, and I think I found a fix which I added to the link in my post. Can you try again?