let’s take a look at the effect first. before css3, this was completely unimaginable. only pictures could do it. but today, when html5 and css3 are so popular, it is not a problem to achieve this effect.
look at the implemented code:
<!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>
![[Web front-end] Node.js quick start](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
