This script forces the rounded version of the layout (which includes some fewer tweaks applied which also improves bugs).
As of
This script was originally made by Magma_Craft (this was before he deleted his script after he archived it), but I re-added this script myself but with fewer tweaks applied to this.
Note: When you install this script on the non-rounded version of YouTube as a cookie setting, it will be forced into the rounded version.
