code: function(paths) {
      return (
          gulp
          .src(paths.src.path)
          .pipe(rework(
              reworkUrl(function (url) {
                  return isRelative(url) ? path.basename(url) : url;
              })
          ))
          .pipe($.if(config.sourcemaps, $.sourcemaps.init({ loadMaps: true })))
          .pipe($.concat(paths.changeExtension(paths.output.name, '.css')))
          .pipe($.if(config.production, $.cssnano(config.css.cssnano.pluginOptions)))
          .pipe($.if(config.sourcemaps, $.sourcemaps.write('.')))
          .pipe(gulp.dest(paths.output.baseDir))
      );
  }
docs: Combine stylesheets.
  
  @param  {GulpPaths} paths
  @return {stream}