Unless you need exactly this theme I would recommend disabling Midnight Lizard with Alt+Shift+L on Facebook and YouTube since both have their own built-in dark themes.
If you want to use Midnight Lizard on those websites anyway then
For YouTube: it should not be changing video at all only thumbnails which can be fixed by changing Image settings (setting everything to 100%)
For Facebook: by default Filter mode is used there. You can try setting Complex mode instead to see if it suits you better