Attributes labeled with the 'common' state will be copied over
to the other states. A 'common' attribute overrides other
states attributes
Since different themes could possibly have different common
attributes, the common attribute set should be reset at the
beginning of theme application. The theme's common attributes
should be added during application.
Common attributes set in code will be removed after a theme is
applied because of the above note. To ensure common attributes
exist theme-by-theme, add those attributes in the theme
building functions instead.