You must not write hooks as comma separated lists of elements like
td#middle-column div.bt, div#middle-column div.bt { ... }in Chameleon themes because the Chameleon engine can't handle these comma lists. Please write two seperate statements instead.
td#middle-column div.bt { ... } div#middle-column div.bt { ... }
A Moodle Theme from Urs Hunkler, unodo and Andrew Walker, Alton College.