Built-in dark mode for web contents

[batata]

I love extensions like Dark Reader that automatically transform any website with a dark theme. The way they do this is by injecting many new styles into the DOM, it works but there is two main drawbacks to this method :
- there's a latency that makes contents blink
- it reduces performances on some websites by a lot

So It would be great if there could be a built-in low level solution (directly in web render?) that would swap colors on the fly without editing the page styles and thus would solve the two aforementioned issues.

[Jon]

(Note: similar ideas have been merged into this thread)