TTM expands the main video view and moves the chat box to the right hand side. Additionally, all other on-screen elements get hidden. All changes revert upon leaving theater mode.
8/22/2023 Note: YT seems to be updating their webplayer multiple times over the last few days and breaking the extension as a result. For now the plan is to react whenever I can until YT stabilizes.
v4.02 Changes: hide/show chat option added
v4.00 Updated June 2023! 🥳🎉 (pre-v4.00 Updated June 2020... 😓)