Setting up the width of your site is easy with KickstartCassiopeia. This article will tell you how this is done.
First off: The Cassiopeia template has the option to set a fluid layout or a default layout. Go to template styles, template, and choose static or fluid layout.
When choosing fluid, the website will take on the width of your screen. Our module does not interfer with this, so you can use it if you so desire.
When choosing static, it has a pre-defined width. KickstartCassiopeia has 2 extra options to change this, and make your site wider, or even more wider than the default width.
You can do this in the module settings, choose the tab General and there you have the option to set the width to default, wider, or widest. This will make your site wider to your likings, allowing for more content, with a fixed layout.