When adding custom content to the panel, it will expand to the edges by default so that you can have full-width content (like the search bar or a map). If you wish to space your content away from the edges, you can make use of these classes:
.shiftnav-content-wrap (25px)
.shiftnav-content-wrap-small (10px)
.shiftnav-tagline (25px padding, larger font size & line-height)
Example:
<div class="shiftnav-content-wrap"> This content will be spaced away from the edges of the panel and will look nicer than if the wrapper class were not present. </div>