!DOCTYPE html>
html>
head>
style type='text/css'>

/* 上三角 */
.arrow-up {
 width: 0;
 height: 0;
 border-left: 20px solid transparent;
 border-right: 20px solid transparent;
 border-bottom: 20px solid green;
}

/* 下三角 */
.arrow-down {
 width: 0;
 height: 0;
 border-left: 20px solid transparent;
 border-right: 20px solid transparent;
 border-top: 20px solid orange;
}

/* 右三角 */
.arrow-right {
 width: 0;
 height: 0;
 border-top: 60px solid transparent;
 border-bottom: 60px solid transparent;
 border-left: 60px solid blue;
}

/* 左三角 */
.arrow-left {
 width: 0;
 height: 0;
 border-top: 10px solid transparent;
 border-bottom: 10px solid transparent;
 border-right: 10px solid silver;
}
/style>
/head>
body>
 div class="arrow-up">/div>
 div class="arrow-down">/div>
 div class="arrow-left">/div>
 div class="arrow-right">/div>
/body>
/html>