📅  最后修改于: 2022-03-11 14:47:52.293000             🧑  作者: Mango
div {
width: 500px;
height: 100px;
position: relative;
padding-top: 20px;
margin-top: 50px;
}
div::before {
content: '';
display: block;
position: absolute;
top: 0;
width: 50%;
left: 25%;
border-top: 1px solid red;
}