实现效果：使用before和after就可以实现，代码量不多，长度颜色都可以自己调整
<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><title>Title</title><style>*{margin:0;padding:0;}html,body{width:100%;height:100%;background:#040d32;}.border-box{position: relative;margin:300px auto;width:400px;height:300px;background: rgba(1, 19, 67, 0.8);border: 2px solid #00a1ff;border-radius: 8px;}.border-box::before {position: absolute;top: -2px;bottom: -2px;left: 30px;width: calc(100% - 60px);
