In the Layout section of the theme options you can setup the maximum width of the site, as well as the default options for the sidebar appearance in various places.
Max Grid width
This is a responsive theme, which means as you view your site on smaller screens, the theme adapts its appearance. The 'Max Grid width' setting set the maximum width which your site's grid can reach. Eg. if you set it at 1200px, the grid will be 1200px wide on a 1920px monitor.When the screen's width is smaller than this setting, it has no effect. Eg. on a tablet with a 768px wide display, the grid will be at a maximum of 768px.
Setting an explicit value in Pixels is recommended, although this field can also accept % values. Setting for example 'Max Grid width' to 100% will make the grid always as wide the browser's window.