改进 YouTube 剧场模式，参考 Twitch.tv 的设计，增强视频与聊天室布局，同时保持性能与兼容性，也达到了类似B站的网页全屏功能。同时新增可选的、自制风格的浮动聊天室功能（仅限全屏模式），融入了 YouTube 原有的设计语言。
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?