function getCssBuild(element) {
  if (cssBuild !== undefined) {
    return /** @type {string} */(cssBuild);
  }
  if (element.__cssBuild === undefined) {
    // try attribute first, as it is the common case
    const attrValue = element.getAttribute(CSS_BUILD_ATTR);
    if (attrValue) {
      element.__cssBuild = attrValue;
    } else {
      const buildComment = getBuildComment(element);
      if (buildComment !== '') {
        // remove build comment so it is not needlessly copied into every element instance
        removeBuildComment(element);
      }
      element.__cssBuild = buildComment;
    }
  }
  return element.__cssBuild || '';
}
Return the polymer-css-build "build type" applied to this element

@param {!HTMLElement} element
@return {string} Can be "", "shady", or "shadow"