css绘制空心圆，被选中时空心变实心

   /*空心圆*/
  .circle{
    display: inline-block;
    border: 1px solid #fff;
    background-color: transparent;
    width: 8px;
    height: 8px;
    border-radius: 50%;
    margin-right: 10px;
  }
  
  /*被选中时变实心圆*/
  .el-menu-item.is-active .circle {
    background-color: #fff !important;
 }