So I have just logged in to edit my website for the first time in a few weeks and as usual I went to Edit Page > Stay in Edit Mode.
When I went to edit a standard text module or the admin/site settings, the editing/settings module itself looks to be completely screwed.
The styling of the editing module seems to be gone, the buttons don't appear properly and most of the boxes/drop downs/text areas/tabs don't even function :(
I have attached a screenshot gallery of the "Site Settings", "Site Management" and standard text editor modules to show how the errors and how it looks:
This is what the Site Settings used to (are supposed to) look like
I'm currently on DNN Platform v8.0.2. However since I haven't logged in or made any changes within the last few weeks, I have no idea when this started.
In February time I did post this thread and carried out the actions from Sebastian's answer, however the editing module were fine way after that. I'm not sure if maybe there are further changes I need to make to the container html files (however what doesn't make sense to me is that there are only errors in the "edit mode" modules)