UX - Disable the toggled checkbox if the maptheme is enabled

[Gustry]

Better UX like this @nboisteault ! It makes it much clearer what to expect. Note that the state of the checkbox is not lost, just disabled. So we don't loose configuration layer per layer.

Side note, if we enable the maptheme on startup, in a better world, the content of the dropdown menu should be updated :

It should be either :

• Follow maptheme
• Disabled

Right ?

[nboisteault]

@Gustry That's it!