Change activation email template

I am using tutor version 10.4.1 and I am unable to update the theme for the activation email as it was made in the red-theme using the base_body.html file.
I placed the file into my custom theming template as it was made in the red-theme:
The email theming works for the native Open edX installation. Using the same template in a tutor installation, I always get the default activation email consisting of the edX logo and the outdated text.

The logs are not showing any errors/useful information.

Does anybody have an idea what I am doing wrong? Maybe I have to place the file somewhere else?

Thanks in advance!

You have to follow the same hierarchical paths when including the base_body.html file in your custom theme.