“With this knowledge, I acquired the help of my good friend Wes Bos. Together we went looking for a way to customize our installs. Luckily enough, the Chromium team have set us up with a nice way of inserting our own CSS.”
Pick any theme and drop it in one of these locations depending on your system:
Mac: ~/Library/Application\ Support/Google/Chrome/Default/User\ StyleSheets/Custom.css
PC: C:\Users\YourUsername\AppData\Local\Google\Chrome\User Data\Default\User StyleSheets\Custom.css
Ubuntu (Chromium): ~/.config/chromium/Default/User\ StyleSheets/Custom.css
Detach your devtools from the window with the button on the bottom left. With devtools still focused, open devtools again (⌥⌘I (Command + Option + I) or Control + Shift + I). Customize any styles on the fly then update your Custom.css file.