When OpenCart says it's coming back, it literally means the template folder, i.e.
/catalog/view/theme/your-theme-name/template/
The stylesheet folder is outside, so you need to add it manually to your <head> theme if you want to include a default stylesheet
EDIT
If you want your stylesheet to be loaded, you need to edit the template in
/catalog/view/theme/your-theme-name/template/common/header.tpl
and change the way there
source share