<div class="wrap">
你好,我是一条线
</div>
div{
box-sizing:border-box;
}
.wrap{
padding:10px;
background-color:#fff;
margin-left: 5xp;
position:relative;
border-radius:5px;
}
.wrap::before{
content:'';
display:block;
background:#3eaf7c;
position:absolute;
z-index:-1;
left:-5px;
top:0;
width:20px;
height:100%;
border-radius:5px 0 0 5px;
}