效果圖：
代碼：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
.start {
width: 0;
height: 0;
margin: 80px auto;
color: #ffffff;
position: relative;
border-right: 100px solid transparent;
border-left: 100px solid transparent;
border-bottom: 70px solid red;
display: block;
transform: rotate(35deg);
}
.start::before {
content: "";
height: 0px;
width: 0px;
position: absolute;
display: block;
top: -45px;
left: -65px;
border-right: 30px solid transparent;
border-bottom: 80px solid red;
border-left: 30px solid transparent;
transform: rotate(-35deg);
}
.start::after {
content: "";
width: 0;
height: 0;
position: absolute;
display: block;
top: 3px;
left: -105px;
border-right: 100px solid transparent;
border-bottom: 70px solid red;
border-left: 100px solid transparent;
transform: rotate(-70deg);
}
</style>
</head>
<body>
<div class="start"> </div>
</body>
</html>