The demos use
Widget Context to show/hide widgets on different parts of the site. All layout changes on the demo are done using this method.
After looking at the demo with
Firebug, it appears that the way to make the "classes" area fit to 3 columns instead of 4 is to find the following code around line 986 of css/editor.css, and change the width from 24% to 32%:
.class_item {
width: 32%;
}