效果图：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title></title>
<style>
.triangle{
display: block;
width: 0px;
height: 0px;
border-left: 15px solid transparent;
border-bottom: 15px solid transparent;
border-right: 15px solid #FF5954;
border-top: 15px solid #FF5954;
}
.check{
display: block;
width: 6px;
height: 12px;
border-color:#fff;
border-style: solid;
border-width: 0 2px 2px 0;
transform: rotate(45deg);
margin:0 auto
}
</style>
</head>
<body>
<div class="triangle"></div>
<div style="width:200px;height200px;background:red;">
<div class="check"></div>
</div>
</body>
</html>
