code: function(opts, done) {
      if (typeof opts !== 'object') {
        done = opts;
        opts = null;
      }
      validateCallback(done);
      this.parse(opts);
      this.renderCSS(done);
      return this;
    }
docs: Renders flat CSS from pruned theme source.
  @param {Function} callback function to run on completion.
  @returns {SassThematic} self reference.