Because I have some light sensitivity issues, I use browser extensions including Dark Reader and Midnight Lizard to enforce my own 'dark mode' across the web.

You can also use extensions like that to set the contrast to a more comfortable level on websites that are already dark.

I highly recommend this if you have light sensitivity issues like me.

Also note that when the contrast on a page is higher, you can generally get away with lower brightness. This is pretty convenient on phones, and probably more necessary as well since on a phone you're more likely to have an OLED screen that really surfaces extreme contrast like white on black.