I second this, either allow to customize theme or allow to use Themes available on Chrome Web store. I use different versions of browsers for my different profiles - work, family, developer and personal. For this I use color mapping - like I use Chrome with a Green theme for my primary personal profile so that the moment I see Green top bar I know I am on my personal workspace. Opera would have been my first choice for browser had it allowed color themes, but since it doesn't at the moment I am using Microsoft Edge and Brave.