效果：
代码：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
body {
padding: 120px;
}
.mainbox {
width: 320px;
height: 320px;
position: relative;
/* 超出隐藏需要加上 */
overflow: hidden;
}
.content {
width: 320px;
height: 320px;
line-height: 320px;
text-align: center;
background-color: #cde;
}
.line {
/* 结合外层元素的相对定位 */
position: absolute;
}
.line:nth-child(1) {
top: 0;
left: 0;
width: 100%;
height: 3px;
/* 加上渐变效果，方可形成拖尾效果 */
background: linear-gradient(90deg, transparent, orange);
animation: animate1 8s linear infinite;
}
/* 分别控制其上下左右的定位距离，从而形成线条跟随效果 */
@keyframes animate1 {
0% {
left: -100%;
}
50%,
100% {
left: 100%;
}
}
.line:nth-child(2) {
top: -100%;
right: 0;
width: 3px;
height: 100%;
background: linear-gradient(180deg, transparent, red);
animation: animate2 8s linear infinite;
/* 注意要加上延时触发动画效果，这样线条才会依次触发 */
animation-delay: 2s;
}
@keyframes animate2 {
0% {
top: -100%;
}
50%,
100% {
top: 100%;
}
}
.line:nth-child(3) {
bottom: 0;
right: 0;
width: 100%;
background: linear-gradient(270deg, transparent, green);
animation: animate3 8s linear infinite;
animation-delay: 4s;
}
@keyframes animate3 {
0% {
right: -100%;
height: 3px;
}
50%,
100% {
height: 2px;
right: 100%;
}
}
.line:nth-child(4) {
bottom: -100%;
left: 0;
width: 3px;
height: 100%;
background: linear-gradient(360deg, transparent, #3a86ff);
animation: animate4 8s linear infinite;
animation-delay: 6s;
}
@keyframes animate4 {
0% {
bottom: -100%;
}
50%,
100% {
bottom: 100%;
}
}
</style>
</head>
<body>
<div class="mainbox">
<span class="line"></span>
<span class="line"></span>
<span class="line"></span>
<span class="line"></span>
<div class="content">线条环绕</div>
</div>
</body>
</html>