Epsilon is based off of delta by roog. I wanted a theme similar to delta that had thicker borders (for resizing) and that picked up the colors from the GTK theme.

Screenshot 1:
Using the Die Hard 4 GTK theme by obscurant.
http://xfce-look.org/content/show.php/Diehard+4+GTK?content=143443

Screenshot 2:
Using the delta GTK theme by roog.
http://xfce-look.org/content/show.php?content=125996

Screenshot 3:
Using Litestyle by weakhead.
http://weakhead.deviantart.com/art/Litestyle-suite-148308075