css实现三角形

<!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">
    <meta name="author" content="杨欣">
    <title>css三角形</title>
    <style>
        .triangle{
            width: 0;
            height: 0;
            border-width: 40px;
            border-style: solid;
            border-color: transparent transparent transparent red;
            /*border-color的四个值代表上右下左，分别实现下左上右箭头 */
        }
    </style>
</head>

<body>
<div class="triangle"></div>
</body>

</html>