A speedy addon for firefox (extension for chrome ) that injects custom grey-ish css in your page when you're roaming on youtube.
Get it from https://addons.mozilla.org/en-US/firefox/addon/dark-youtube-theme
or: https://chrome.google.com/webstore/detail/dark-youtube-theme/djhcepodfooinnfhfccmoeabagbjchhg
Disclaimer:
I got that main icon from https://www.iconfinder.com/icons/104445/video_youtube_icon, it was created by Picons.me and it's free for commercial use.
I got the puppy eyes icon from http://thenounproject.com/term/puppy-eyes/30086/, it was created by Joe Shelton and it's licensed under CC Attribution 3.0 (CC BY 4.0)
I DO NOT OWN the rights for the poster i'm currently using in the crome store, but I wasn't able to find the owner to ask for his permission so far. Any hint is highly appreciated !