The most recent designs are using even more full width sections to show everything. Sometime the background color or image is full width but the content is boxed and limited to a standard max-width, and sometimes the content is as large as the page (example for a slideshow). You can do all that with ui/Theme-Builder.
This article will explain you how to do that.

On each section you can choose how do you want it to be:

• Section full width? ('Yes' by default)

Choose 'Section full width?' to 'No' now you can set a container max-width to wrap the main content.

• Default
• X-Small
• Small
• Large
• Expand