Only with a script: https://greasyfork.org/en/scripts/13183-myanimelist-mal-move-favorites
Install a browser extension like Stylus and then check out a site like https://userstyles.org/styles/browse/reddit or https://freestyler.ws/search?q=reddit to find themes. The only downside to this is that a lot of themes are not up to date, so you will inevitably find things that don't look right. But hey, this is /r/webdev and these are stylesheets. You can always fix them!
Yes, I've been trying to make a CSS that does something like it, with almost-success, it would take some further refinement. But it just could be that there was a userscript that would fix it, and maybe less prone to break as YT changes its CSS. There are a couple of userstyles on those sites that distribute them, but it seems all are at least a few years old and no longer work.
Here's what I got so far, if anyone's interested:
​
#secondary-inner, ytd-comments, #commentsDiv, #logoTagDiv, #utilDiv, #gNavDiv, #gNavBottom, #otherVidsDiv, #actionsAreaDiv, #ratingAndStatsDiv, #asDiv, #vrParentDiv, #footerDiv, #ticker, #leaderboardAd, #footer, #copyright, #masthead, #vidTitle { display: none !important; }
I think it's almost all taken from a somewhat obscure userstyle site I've stumbled upon, but adding a bit more stuff and removing lots of other stuff. I think it was this one, even though I thought it was 2014-ish or so, while this is from 2008. https://freestyler.ws/style/4696/youtube-vid-only-makes-video-take-up-whole-page
Hm. Any suggestions? I find it fine and I'm here hours upon hours. Is it the countless gradients? Would maybe something like this be good?