AssetResolver::getCssAssets

public AssetResolver::getCssAssets(AttachedAssetsInterface $assets, $optimize)

public function getCssAssets(AttachedAssetsInterface $assets, $optimize) {
  $theme_info = $this->themeManager->getActiveTheme();
  // Add the theme name to the cache key since themes may implement
  // hook_library_info_alter().
  $libraries_to_load = $this->getLibrariesToLoad($assets);
  $cid = 'css:' . $theme_info->getName() . ':' . Crypt::hashBase64(serialize($libraries_to_load)) . (int) $optimize;
  if ($cached = $this->cache->get($cid)) {
    return $cached->data;
  }

  $css = [];
  $default_options = [
    'type' => 'file',
    'group' => CSS_AGGREGATE_DEFAULT,
    'weight' => 0,
    'media' => 'all',
    'preprocess' => TRUE,
    'browsers' => [],
  ];

  foreach ($libraries_to_load as $library) {
    list($extension, $name) = explode('/', $library, 2);
    $definition = $this->libraryDiscovery->getLibraryByName($extension, $name);
    if (isset($definition['css'])) {
      foreach ($definition['css'] as $options) {
        $options += $default_options;
        $options['browsers'] += [
          'IE' => TRUE,
          '!IE' => TRUE,
        ];

        // Files with a query string cannot be preprocessed.
        if ($options['type'] === 'file' && $options['preprocess'] && strpos($options['data'], '?') !== FALSE) {
          $options['preprocess'] = FALSE;
        }

        // Always add a tiny value to the weight, to conserve the insertion
        // order.
        $options['weight'] += count($css) / 1000;

        // CSS files are being keyed by the full path.
        $css[$options['data']] = $options;
      }
    }
  }

  // Allow modules and themes to alter the CSS assets.
  $this->moduleHandler->alter('css', $css, $assets);
  $this->themeManager->alter('css', $css, $assets);

  // Sort CSS items, so that they appear in the correct order.
  uasort($css, 'static::sort');

  // Allow themes to remove CSS files by CSS files full path and file name.
  // @todo Remove in Drupal 9.0.x.
  if ($stylesheet_remove = $theme_info->getStyleSheetsRemove()) {
    foreach ($css as $key => $options) {
      if (isset($stylesheet_remove[$key])) {
        unset($css[$key]);
      }
    }
  }

  if ($optimize) {
    $css = \Drupal::service('asset.css.collection_optimizer')->optimize($css);
  }
  $this->cache->set($cid, $css, CacheBackendInterface::CACHE_PERMANENT, ['library_info']);

  return $css;
}