.view>div:nth-child(1)>div {
          width: 100%;
          line-height: 40px;
          text-align: center;
          position: relative;
        }
        .view>div:nth-child(1)>div:hover { /*只是做一个示例，真实中可不是hover*/
          color: red;
          background-color: #ffffff;
        }
        .view>div:nth-child(1)>div:hover::before {
          content: '';
          display: block;
          position: absolute;
          left: 0px;
          top: 0px;
          bottom: 0px;
          width: 4px;
          background-color: red;
         
        }