code: def remove_custom_css(destdir, resource=PKGNAME ):
      
  
      # Remove the inclusion in the main CSS
      if not os.path.isdir( destdir ):
          return False
      custom = os.path.join( destdir, 'custom.css' )
      copy = True
      found = False
      prefix = css_frame_prefix(resource)
      with io.open(custom + '-new', 'wt') as fout:
          with io.open(custom) as fin:
              for line in fin:
                  if line.startswith( prefix + 'START' ):
                      copy = False
                      found = True
                  elif line.startswith( prefix + 'END' ):
                      copy = True
                  elif copy:
                      fout.write( line )
  
      if found:
          os.rename( custom+'-new',custom)
      else:
          os.unlink( custom+'-new')
  
      return found
docs: Remove the kernel CSS from custom.css