Stable version (5.2.1168.74)

[tamer]

Or instead you can simply add this to your custom.css here chrome://settings/cbCustomCss

Code:

body.neterror {
  --background-color: #111;
  --google-gray-900: #fefefe;
  --primary-button-fill-color: #225fc3;
}

And it should work for all the internal error pages listed here: chrome://network-errors


ps: It would be great if devtools also supported custom.css since they deprecated applyStyleSheet api in recent versions. Now you need to recompile it separately just to change the font and remove these annoying tabs close buttons.