# File lib/compass/commands/watch_project.rb, line 125
      def remove_obsolete_css(base = nil, relative = nil)
        compiler = new_compiler_instance(:quiet => true)
        sass_files = compiler.sass_files
        deleted_sass_files = (last_sass_files || []) - sass_files
        deleted_sass_files.each do |deleted_sass_file|
          css_file = compiler.corresponding_css_file(deleted_sass_file)
          remove(css_file) if File.exists?(css_file)
        end
        self.last_sass_files = sass_files
      end