Adam, thanks for your reply. Unfortunately it doesn't solve the problem. Maybe I didn't explain it well.

The editor is working correctly and includes the CSS as it is suppose to do.

The problem is with the Insert Template module. When previewing a template, the CSS file is not linked to the right panel, so if I have 10 templates with a background color difference, the user cannot see it while selecting the template.

 

Below is a template as it appears correctly in the editor and the same template in the Templates selection tool, notice the nmissing box, fonts and background color.