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);
