code: function(width) {
      document.cookie = 'preview-width=' + width;
      forEach(resizeableEls, function(el) {
        if (width === 'auto') width = el.parentNode.offsetWidth;
        el.style.width = width + 'px';
        // TODO: Add CSS transitions and update height after `transitionend` event
        postMessage(el.getElementsByTagName('iframe')[0], 'getHeight');
      });
    }
docs: `.resizeable` padding