readSharedStyle_(node, objectStack) {
    const id = node.getAttribute('id');
    if (id !== null) {
      const style = readStyle.call(this, node, objectStack);
      if (style) {
        let styleUri;
        let baseURI = node.baseURI;
        if (!baseURI || baseURI == 'about:blank') {
          baseURI = window.location.href;
        }
        if (baseURI) {
          const url = new URL('#' + id, baseURI);
          styleUri = url.href;
        } else {
          styleUri = '#' + id;
        }
        this.sharedStyles_[styleUri] = style;
      }
    }
  }
@param {Element} node Node.
@param {Array<*>} objectStack Object stack.
@private