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This script will revert all UI changes prior to late 2022 (which disables rounded corners on everything and reverts 2019-2022 backgrounds.)
< 脚本 YouTube - Revert UI changes before late-2022 (Non-Rounded Design) 的反馈
Unfortunately this causes the video to keep summoning the fullscreen video title at the top edge. Also causes the options and CC selector, page options etc to exit quickly. If you want to change quality, adjust subtitles, you better do it fast and click fast or you have to click the gear icon again.