Function scopeShadowCss

src/shadow-embed.js:215–241

(shadowRoot, css)

 * @visibleForTesting
 */
export function scopeShadowCss(shadowRoot, css) {
  const id = devAssert(shadowRoot['id']);
  const doc = shadowRoot.ownerDocument;
  let rules = null;
  // Try to use a separate document.
  try {
    rules = getStylesheetRules(doc.implementation.createHTMLDocument(''), css);
  } catch (e) {
    // Ignore.
  }
  // Try to use the current document.
  if (!rules) {
    try {
      rules = getStylesheetRules(doc, css);
    } catch (e) {
      // Ignore.
    }
  }

  // No rules could be parsed - return css as is.
  if (!rules) {
    return css;
  }

  // Patch selectors.
  return ShadowCSS.scopeRules(rules, `.${id}`, transformRootSelectors);
}

/**
 * Replaces top-level selectors such as `html` and `body` with their polyfill