XF 1.5 Screen Width

My brand-new vanilla installation doesn't look that great on my iPhone 6. I have all this dead space that makes my text super small.


The xenForo forum looks much better:


What can I change to make mine look like xenForo? Is it an add-on?
Thanks for your reply. I did have responsive design enabled, but I needed to change "width" to "max-width" in Style Properties: General: Page Width Controller.

Works great now!