code: function themeBuildStream() {
    // Make a copy so that we don't modify the actual config that is used by other functions
    var paths = config.themeBaseFiles.slice(0);
    config.componentPaths.forEach(component => paths.push(path.join(component, '*-theme.scss')));
    paths.push(config.themeCore);
  
    return gulp.src(paths)
    .pipe(concat('default-theme.scss'))
    .pipe(utils.hoistScssVariables())
    .pipe(sass())
    .pipe(dedupeCss())
    // The PostCSS orderedValues plugin modifies the theme color expressions.
    .pipe(minifyCss({orderedValues: false}))
    .pipe(utils.cssToNgConstant('material.core', '$MD_THEME_CSS'));
  }
docs: builds the theming related css and provides it as a JS const for angular