Width: 98% of the window width. The display ratio is 1:2, so that people with 16:9 displays don't get the whole page filled with video! Let me know if this is a problem.

This makes the "large player" button make the video widescreen but still lets you browse the comments, shows the current playlist, sidebar, etc. None of the shifting/bugginess of any of the other extensions/scripts I've tried!


Known bugs:

Probably not going to fix as it would take many many hours:
-Progress bar doesn't fit
-Annotations not scaled with video frame

Probably will fix soon:
-Background wrong colour
For now, I recommend https://chrome.google.com/webstore/detail/dark-skin-for-youtube/bfeknfgchonpnofdjokchhdhdnddhglm


Tested on May 16, 2015, Chrome version 42.0.2311.152 m. No special instructions - just install and enjoy!