改善 YouTube 劇場模式，參考 Twitch.tv 的設計，增強影片與聊天室佈局，同時維持效能與相容性。另新增可選的、自製風格的浮動聊天室功能（僅限全螢幕模式），與 YouTube 原有的設計語言相融合。
Very interesting suggestion, I will look into this idea. In the mean time, it seems that the script you linked can be used in tandem with this script to achieve the effect you want, but it seems it does break when the chat is showing and scrolling is broken in fullscreen.
Alright added the stuff you wanted. Not super sure how resilient the new features will be against YouTube's constant unnecessary updates. But do tell me if anything is broken.
Would it be possible to move the header below the video, similar to https://github.com/Zren/ResizeYoutubePlayerToWindowSize?