- @yann300 asked for more visible buttons, provided black border

Refs: #1657

 - Existing themes aren't broken
 - New theme provides good color scheme
 - Buttons are visible and clearly defined

 - Prevent excessively verbose stylesheet

Two existing themes retain their styling, though the cssjs now
checks whether a few properties are set to custom: true on the
current style, if so passes the value, otherwise returns the
existing default

Ref: #1198