Some of the HTML5 themes are designed to fill the entire width of the browser window. To change the width of the theme, you will need to edit the site's default.css file.
Typically, the style that you will want to edit is the #mainContainer style. However, be aware that different themes may have this style under a different name so you will need to experiement a bit until you find the right style.
Please Note
The information in this article is provided solely as a courtesy and to offer basic instructions on making very simple changes to your store's HTML templates.
Please understand that - regardless of how simple the changes may be - HTML changes and troubleshooting fall outside the scope of our support department. The 3dcart support team is neither trained, qualified, nor allowed to make these changes for you. The boundary of our scope in this matter is limited to providing these instructions and helping you reset the template if the changes don't work as you wanted.
If you are uncomfortable with making changes to your site's HTML, please contact your sales representative and inquire about our HTML and design services which can make these changes for you.
Thank you for your understanding