It probably wasn't clear in my post but I'd be happy with the toggle being in the browser (not something I've historically thought about but a great idea), it was more about the existence of a toggle.
I do agree with @jaredwhite@humansare.social that having the toggle in the header is a waste of space. Same with horizontal tabs.
Do you mean altogether unnecessary, or unnecessary as a persistent toggle on the main screen?
If you're talking about the former I'd disagree, easiest way to explain is with my own real-world example.
I put basically everything in dark mode, but our ticketing system's website I put in light mode (even though they have a dark mode) because their dark mode looks like shit.
100% correct. Unfortunately I'm far more likely to have access to a toggle than for them to make their dark mode nice.
E.g. I've asked them to add more languages to the code button in their WYSIWYG editor for replying to tickets. I don't use/do any web stuff but I had figured out that they use Froala, and Froala uses prism.js. I asked them to include 5 more languages (bash/sh/shell, batch, ini, json, Powershell) and requested that the list be sorted alphabetically, and told them it should just be a matter of changing the Froala
codeSnippetLanguageplugin option. I haven't even had a reply in 5 months.I also spent some time trying to modify the WYSIWYG editor options myself using a userscript but didn't get anywhere useful.