It can be annoying and visual jarring if you prefer dark theme for other apps, but pages in your web browser are light themed.
There are a few different solutions you can try.
Putting Chrome in dark mode.
Issue with white effect in YouTube making it hard to read the controls at the bottom.
The fix seemed to work for me found here.
In chrome://flags, set “enable dark mode on web elements” to “enabled with selective inversion of non-image elements”.
This seems to be the best looking dark theme plugin I have tried.
There is a potential security risk as this plugin will have access to data in your pages.