triangle.html

<!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>css制作三角形</title>
    <style type="text/css">
    .wrap>div{
     display: inline-block
    }
    #triangle-up {
        width: 0;
        height: 0;
        border-left: 50px solid transparent;
        border-right: 50px solid transparent;
        border-bottom: 100px solid red;
    }
    #triangle-down {
        width: 0;
        height: 0;
        border-left: 50px solid transparent;
        border-right: 50px solid transparent;
        border-top: 100px solid red;
    }
    #triangle-left {
        width: 0;
        height: 0;
        border-top: 50px solid transparent;
        border-right: 100px solid red;
        border-bottom: 50px solid transparent;
    }
    #triangle-right {
        width: 0;
        height: 0;
        border-top: 50px solid transparent;
        border-left: 100px solid red;
        border-bottom: 50px solid transparent;
    }
    #triangle-topleft {
        width: 0;
        height: 0;
        border-top: 100px solid red;
        border-right: 100px solid transparent;
    }
    #triangle-topright {
        width: 0;
        height: 0;
        border-top: 100px solid red;
        border-left: 100px solid transparent; 
    }
    #triangle-bottomleft {
        width: 0;
        height: 0;
        border-bottom: 100px solid red;
        border-right: 100px solid transparent;
    }
    #triangle-bottomright {
        width: 0;
        height: 0;
        border-bottom: 100px solid red;
        border-left: 100px solid transparent;
    }
    </style>
</head>
<body>
    <div class="wrap">
        <div id="triangle-up"></div>
        <div id="triangle-down"></div>
        <div id="triangle-left"></div>
        <div id="triangle-right"></div>
    </div>
    <div class="wrap">
        <div id="triangle-topleft"></div>
        <div id="triangle-topright"></div>
        <div id="triangle-bottomleft"></div>
        <div id="triangle-bottomright"></div>
    </div>
</body>
</html>