Traverse up the dom to find sticky parent

sticky.ts

/**
 * Traverse up the dom to find a sticky parent node crossing any shadow boundaries
 */
export function findStickyParent(element: HTMLElement): HTMLElement | null {
  let elm = element.parentNode || element.host;

  while (elm) {
    if (elm.style && elm.style.top && window.getComputedStyle(elm).position === `sticky`) {
      return elm;
    }
    elm = elm.parentNode || elm.host;
  }
  return null;
}