The design template is defined by the preset options of the Style Editor - including colors, configuration classes, and in some cases, additional CSS.
There are more than 20 preset styles, and you can change the design of your website from one to another without modifying any HTML or CSS, simply by selecting one of the preset templates available under Matrix Framework → Templates
To change the template:
You can further customize the template by changing the configuration classes for the navigation, content, footer, and other sections.