Use Twitch's built in vertical theater layout at larger window sizes
Twitch actually has a built in vertical layout in theater mode, but the catch is it only activates with a window width less than 920px. This is a quick and dirty hack that works by overwriting the browser's reported width so that twitch will use the vertical layout under any arbitrary threshold. By default it is set to 1440px and under, but you can simply edit the thresholdWidth variable to adjust to whatever you'd like.
One of the main benefits this has over alternate solutions is you can see the stream details (user, title, viewer count, etc.) when hovering your mouse over the player, thanks to it being the theater mode player. Also it doesn't constantly break the page layout like other solutions I've tried.
Note: Only works in theater mode
