To help focus better on the actual content of a page, say a documentation page or an article. Just blur out the distracting content
Written as an IIFE this can easily be embedded via Tampermonkey or Greasemonkey but it could just as well be included in a script tag. Also copy&paste into development console is an option. Next step will be a chromium extension for easier use.
Press Alt-J to start. Then select elements to blur out with mouse click. Remove blur by clicking again. Press Alt-K to toggle Control Panel. Length determines the intensity of the blur. Brightness determines whether to darken the element. Press Alt-L to reset blur.