實現原理
先畫一個半圓，利用僞類把半圓放在border上
代碼
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
<style>
html, body{
width: 100%;
height: 100%;
}
.father{
width: 400px;
height: 200px;
}
.bule{
width: 100%;
height: 50%;
background: blue;
border-radius: 10px 10px 0 0;
}
.white{
width: calc(100% - 2px);
height: 50%;
background: #fff;
border: 1px solid red;
border-top: 0;
}
.main{
width: 100%;
height: 70%;
text-align: center
}
.butt{
width: 90%;
height: calc(30% - 1px);
text-align: center;
border-top: 1px solid red;
margin: 0 auto;
position: relative;
}
.butt::before{
content: '';
width: 10px;
height: 20px;
position: absolute;
border: 1px solid red;
border-radius: 0 20px 20px 0;
border-left: 1px solid #fff;
position:absolute;
left: -21px;
top: -10px;
}
</style>
</head>
<body>
<div class="father">
<div class="bule"></div>
<div class="white">
<div class="main">main</div>
<div class='butt'>butt</div>
</div>
</div>
</body>
</html>
效果：
