This is my attempt at porting a rounded skin from ButtonFacade's Trinity Suite over to BuffSkin. It's occured to me there's no Round Skins for BuffSkin and that makes Skunk a sad Panda.
There are some limitations- obviously the buffs and debuff colors are already chosen for you, and so on, but if you're handy with an image editor, you're more than welcome to recolor them to your liking.
I've managed to solve the problem of getting this skin to round off buffs (with some coaching from BuffSkin's Author), but I have to confess it's kinda an awkward solution.
In order for the skin to make the buff appear round, the skin must be sized larger than the buff. This can only presently be accomplished by manually adjusting BuffSkin's "Offset" setting in the Interface Options panel for it.
Currently, the ideal setting I have found for the offset is 6.
This will also have the side effect of making the composite buff image (that being the buff Icon plus the overlaid skin) appear larger than it might otherwise be. As such, you may have to adjust sizing or spacing in Buffed! to account for this.
Given those concessions, it does work, it's just not particularly user-friendly. And at the moment this is something I can do little about- the options simply don't exist.