On our newer courses have a button in the editor where you can switch the theme to a white background, which may help
Also, there are extensions for Chrome. I searched for chrome extension to change contrast of colours in google and some popped up. Make sure you vet each one somehow, for safety and usefulness before using. (Using the devtools, you could do it after some fiddling, but'd have to do it each and every time you went to a page. I supposed you could write a script, but although maybe fun, it'd be tough to create one that's useful and robust).