1、在文件夹中创建html页面
2、在html页面中创建div盒子：
<div class="border-anim">
<div class="border-anim-content"></div>
</div>
3、在style标签中添加css样式代码：
<style>
:root {
--border-anim-size: 10em;
--border-anim-width: calc(var(--border-anim-size) / 20);
--border-anim-width-double: calc(var(--border-anim-width)*2);
--border-anim-duration: 5s;
--border-anim-border-color: #1dad23;
--border-anim-hover-color: LightCoral;
}
.border-anim {
width: var(--border-anim-size);
height: var(--border-anim-size);
position: relative;
border: 1px solid var(--border-anim-border-color);
}
.border-anim::before,
.border-anim::after {
content: '';
position: absolute;
border: var(--border-anim-width) solid var(--border-anim-border-color);
/* 让边框在内容区域内绘制 */
box-sizing: border-box;
transition: background-color 1s;
}
.border-anim::before {
animation: anim-border-run calc(var(--border-anim-duration) * 2) linear infinite;
}
.border-anim::after {
animation: anim-border-run calc(var(--border-anim-duration) * 2) calc(var(--border-anim-duration) / -1) linear infinite;
}
.border-anim-content {
width: calc(100% - var(--border-anim-width-double));
height: calc(100% - var(--border-anim-width-double));
margin: var(--border-anim-width);
border: 1px solid var(--border-anim-border-color);
}
@keyframes anim-border-run {
/* 这里将动画分成了4步；也可以改为2步，这时before和after用的就要是两套keyframes了 */
from,
to {
width: var(--border-anim-width-double);
height: 100%;
top: 0;
left: 0;
}
25% {
width: 100%;
height: var(--border-anim-width-double);
top: calc(100% - var(--border-anim-width-double));
left: 0;
}
50% {
width: var(--border-anim-width-double);
height: 100%;
top: 0;
left: calc(100% - var(--border-anim-width-double));
}
75% {
width: 100%;
height: var(--border-anim-width-double);
top: 0%;
left: 0%;
}
/* 需要设置临界效果，否则会渐变 */
from,
to,
24.9% {
border-left-color: var(--border-anim-border-color);
border-top-color: transparent;
border-right-color: transparent;
border-bottom-color: var(--border-anim-border-color);
}
25%,
49.9% {
border-left-color: transparent;
border-top-color: transparent;
border-right-color: var(--border-anim-border-color);
border-bottom-color: var(--border-anim-border-color);
}
50%,
74.9% {
border-left-color: transparent;
border-top-color: var(--border-anim-border-color);
border-right-color: var(--border-anim-border-color);
border-bottom-color: transparent;
}
75%,
99.9% {
border-left-color: var(--border-anim-border-color);
border-top-color: var(--border-anim-border-color);
border-right-color: transparent;
border-bottom-color: transparent;
}
}
</style>
4、实现效果
