I added a little .css file " .config/gtk-3.0/gtk.css" copied below. (there's actually a couple approaches I took, the one I'm using here is not commented out).
/* Two different approaches given below both valid but with slightly different behaviour */
/* This first approach aggressively radiuses everything, even items within the panels themselves. */
/*.xfce4-panel { border-bottom-left-radius: 16px; border-bottom-right-radius: 16px; border-top-left-radius: 16px; border-top-right-radius: 16px; } */
/* This approach is not as aggresive as above. Will need to add some transparent seperators on either end for the radius to show. (16 px for full radius at my current settings) */
.xfce4-panel#XfcePanelWindow { border-radius: 16px; } @import 'colors.css';
For some reason, the formatting is not being preserved here in my cut-and-pasted script. If you can't untangle it, let me know.