code: function getStyle (vnode, checkChild) {
    var res = {};
    var styleData;
  
    if (checkChild) {
      var childNode = vnode;
      while (childNode.componentInstance) {
        childNode = childNode.componentInstance._vnode;
        if (
          childNode && childNode.data &&
          (styleData = normalizeStyleData(childNode.data))
        ) {
          extend(res, styleData);
        }
      }
    }
  
    if ((styleData = normalizeStyleData(vnode.data))) {
      extend(res, styleData);
    }
  
    var parentNode = vnode;
    while ((parentNode = parentNode.parent)) {
      if (parentNode.data && (styleData = normalizeStyleData(parentNode.data))) {
        extend(res, styleData);
      }
    }
    return res
  }
docs: parent component style should be after child's
  so that parent component's style could override it