Goal: To be able to locate elements in HTML using structural pseudo-class selectors
The 4th and 8th commonly used in web pages, we found that they are all multiples of 4, then use 4n to select them.
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
/* ** 偶数 */
/* li:nth-child(2n) { */
/* *** 奇数 */
/* li:nth-child(2n+1) { */
/* 找到前3个 */
/* li:nth-child(-n+3) { */
/* *** 4的倍数 */
li:nth-child(4n) {
background-color: green;
}
</style>
</head>
<body>
<ul>
<li>这是第1个li</li>
<li>这是第2个li</li>
<li>这是第3个li</li>
<li>这是第4个li</li>
<li>这是第5个li</li>
<li>这是第6个li</li>
<li>这是第7个li</li>
<li>这是第8个li</li>
</ul>
</body>
</html>