.scrollbar {
  position: absolute;
  width: 6px;
  right: 0;
  top: 0;
  bottom: 0;
  background-color: #fff;
}
.scrollbar > div {
  height: 100%;
  position: relative;
  background-color: #fff; /* firefox中滚动出现小黑点的bug */
}
.scrollbar > div > span {
  position: absolute;
  top: 0;
  left: 1px;
  right: 1px;
  background-color: #ccc;
  border-radius: 4px;
  cursor: pointer;
}