How can I automatically adjust the brightness of my screen when switching between dark and light sources?

Question

Often I will have my brightness set for a dark-mode website, but when I click an outside link I get blinded by the pure white background. Usually turning down the brightness by a "notch" on my laptop (i.e. Fn+F11) is sufficient for my eyes.

For me this is mostly a browser-based issue but a general solution would be fine too.

Thanks.