This is a copy of Stormi's "Global dark style - changes everything to DARK" (http://freestyler.ws/style/72387/global-dark-style-changes-everything-to-dark). I changed the borders and text colors.

For YouTube, set the main theme in Light, click on your profile, "Appearance", "Light"

As the original creator said, this may not work on all the websites, if you don't like the result on a page, just exclude the page.

To exclude a page: Click on the addon, move your cursor over the title of this theme, click on the wrench button, click on "Do not apply style for this page" and "Aply"