Button corner CSS tweaks.
Button corner CSS tweaks.

Changes suggested by Matt to get closer to image assets.

Self-reviewed.

jrwren/juju-gui,mitechie/juju-gui,CanonicalJS/juju-gui,jrwren/juju-gui,mitechie/juju-gui,mitechie/juju-gui,jrwren/juju-gui,jrwren/juju-gui,CanonicalJS/juju-gui,bac/juju-gui,bac/juju-gui,mitechie/juju-gui,bac/juju-gui,bac/juju-gui,CanonicalJS/juju-gui