Short answer
YouTube's own ambient mode only works in dark theme and is very soft, and YouTube changes the video quality as it likes. The ytModify extension adds a stronger glow that works in full screen, and keeps the quality you choose for each view.
Two small things make YouTube feel worse than it should: the glow around the video is barely there, and the quality keeps dropping to something blurry.
What YouTube gives you
Ambient mode adds a soft glow around the video in the colours of what's playing. Turn it on from the gear icon under a video, but it only shows in dark theme, it's very faint, and it switches off in full screen.
Video quality can be set for one video from the same gear icon. For all videos, YouTube's settings only offer broad choices like Higher picture quality or Data saver, not a fixed resolution.
A stronger glow, and the quality you choose
ytModify is a free Chrome extension I put together for this. It adds:
- Ambient light that follows the video's colours, in normal view and full screen. It can also hide black bars.
- A fixed quality for each view, for example 1080p in full screen, 720p normally and 360p in the mini player.
- A bigger player, YouTube's own font and coloured highlights.
- Auto pop-out: the video floats in a small window when you switch tabs.
Everything is set from one small window, and changes show up straight away. Press G while watching to turn the glow on or off.
Add it to Chrome
Download it from the ytModify page, unzip it, open chrome://extensions, turn on Developer mode and click Load unpacked. The page shows each step.