<div class="div1">实现左边竖线</div>

 .div1 {
        width: 200px;
        height: 50px;
        line-height:50px;
        text-align: center;
        background: #ccc;
        position: relative;
  }

 .div1::before {
        content: "";
        width: 5px;
        height:50px;
        position: absolute;
        top: 0;
        left: 0;
        background: red;
    }

    /* 内阴影 */
    .div1{
        box-shadow:inset 5px 0px 0 0 red;
    }

    /* 外阴影  有些Chrome（比如：Chrome/70.0）版本上会底部1px兼容性问题，显示效果如下图*/
    .div1{
        box-shadow:-5px 0px 0 0 red;
    }

.div1{
   filter:drop-shadow(-5px 0 0 red); 
 }

 .div1 {
    background-image: linear-gradient(90deg, red 0px, red 5px, transparent 5px);
  }