I wonder if anything changed in meantime. I was looking for dark mode recently but I didn't find it. I have feeling I had it in Firefox, it's gone after cleaning cookies, temp ect. But I'm not 100% sure now. Anyway it would look so much better as dark page (without addons for web browser).
"Stylus" fixed the issue for me, somebody already configured a darkmode-design in this browser extension for garmin connect website. Just get the extension, activate it on the garmin connect page and scan for styles. Only one existing as of yet but it works for me.
