Problem

When I tried to change the HTML of my Django app, it didn’t work. However, if I wanted to change the CSS with a separate style, there was no problem…

Solution

I had probably run a command for the production deployment that put the template files of my different apps into a single folder.

The issue is that this folder then takes priority over my app’s templates.
So you need to delete the templates from this folder to take back control of the project.