Problems Replacing Background Color with Static Background Image in Responsive Design

In your CSS you will need to add:

.js .active-nav .content-wrap,
.active-sidebar .mask-right{
  background-image: url('http://dappledthings.me/wp-content/uploads/2013/07/bg4.png') !important;
}

.off-canvas-nav {background: url('http://dappledthings.me/wp-content/uploads/2013/07/bg4.png')important;}