At one time I had put together a Chrome extension for NetSuite in Dark mode. I found an easier way was to go to: chrome://flags/ and then search for the Experimental Dark Mode and enable that.
This was the previous method I used that was a crude CSS override:
WIP Chrome Extension for NetSuite Debugger Dark Mode:
NetSuite_Debugger_Dark_Mode-chrome-ext
To install navigate to
chrome://extensions
and drag and drop zip file.