Chrome 73 comes with the support of Mac Dark Mode - if you've set your Mac OS run on the dark mode, Chrome will get that automatically. That also means you can't turn it off, not from Chrome's setting page.
Here is the magic script to revert that. Copy and paste in your terminal, and restart your Chrome.
defaults write com.google.Chrome NSRequiresAquaSystemAppearance -bool YES
I'm using different browsers for different settings - Chrome for work, Firefox for personal. Firefox got early support of the dark mode, so my Firefox had been running on dark mode and Chrome on bright mode, very distinguishable even with dozens of windows & tabs open.
Chrome 73 broke the pattern and didn't provide a way to revert, so.