Editing the CSS of a theme in PrestaShop is not the easiest thing in the world to do. You have to ftp into the site and use a code editor to edit them currently. If you ever upgrade your theme all of your changes will be erased. This is not ideal.
Our module fixes this. It will allow you to edit the CSS of your site and store the edits on the database so they will not be affected when you upgrade your site or your theme. It also takes advantage of syntax checking and highlighting as well.
If you have any trouble with the module or want to suggest any changes to it you can contact us at dh42 PrestaShop Support
The module is hosted on our site with more info at PrestaShop CSS Module