Lett Web Dimmer

This extension is especially helpful for websites that don't support dark mode, it allows you to adjust the brightness level down to the level that suits you best. The extension is fully private and works in several modes allowing you to: - Enable it on specific websites only. - Enable it on all websites and disable it on some. - Enable it on all websites and use custom settings on some. If you wish to enable it on local files such as PDF files, go to: Extensions > Details > Allow access to file URLs

Screenshots from Chrome Web Store