.post-container:nth-child(even) {
background-color: #f2f2f2;
}<!DOCTYPE html>
<html>
<head>
<title> My Blog </title>
<link rel="stylesheet" type="text/css" href="styles.css">
</head>
<body>
<div id="header">
<div class="container">
<a id="header-title" href="index.html">My Blog</a>
<ul id="header-nav">
<li><a href="about.html">About Me</a></li>
<li><a href="mailto:a@yahoo.com">Email Me</a></li>
</ul>
</div>
</div>
<div id="content">
<div class="post-container">
<div class="post">
<div class="post-author">
<img src="aj1.jpg">
<span>Me</span>
</div>
<p class="post-date">Today</p>
<h3 class="post-title"><em><strong>First Decent Looking Webpage</strong></em></h3>
<div class="post-content">
<p>This is all a test to see if everything is coming out ok.</p>
<p>Just more random text to see how it all turns out</p>
<p>Click <a href="https://www.youtube.com">here</a> for my favorite website!</p>
</div>
</div>
</div>
</div>
<div id="content">
<div class="post-container">
<div class="post">
<div class="post-author">
<img src="jim.jpg">
<span>Jim</span>
</div>
<p class="post-date">Today</p>
<h3 class="post-title"><em><strong>Trying to beat the Gold Challenge</strong></em></h3>
<div class="post-content">
<p>I think I <em>nailed</em> the gold challenge for this test.</p>
</div>
</div>
</div>
</div>
</body>
</html>我使用 Mimo 做了一个 CSS 、HTML 教程，在尝试完成其中一个黄金挑战后，我遇到了一个问题。我按照步骤去了发球台，它不起作用。2 篇博客文章之间应该有一个颜色差异，这将分隔网站上的帖子。
不要使用与 ID 相同的名称，而是向这些div 添加一个类，并将其用作引用来获取这样的nth-child
.post:nth-child(even) .post-container {
background-color: #f2f2f2;
}<!DOCTYPE html>
<html>
<head>
<title> My Blog </title>
<link rel="stylesheet" type="text/css" href="styles.css">
</head>
<body>
<div id="header">
<div class="container">
<a id="header-title" href="index.html">My Blog</a>
<ul id="header-nav">
<li><a href="about.html">About Me</a></li>
<li><a href="mailto:a@yahoo.com">Email Me</a></li>
</ul>
</div>
</div>
<div id="content" class="post">
<div class="post-container">
<div class="post">
<div class="post-author">
<img src="aj1.jpg">
<span>Me</span>
</div>
<p class="post-date">Today</p>
<h3 class="post-title"><em><strong>First Decent Looking Webpage</strong></em></h3>
<div class="post-content">
<p>This is all a test to see if everything is coming out ok.</p>
<p>Just more random text to see how it all turns out</p>
<p>Click <a href="https://www.youtube.com">here</a> for my favorite website!</p>
</div>
</div>
</div>
</div>
<div id="content" class="post">
<div class="post-container">
<div class="post">
<div class="post-author">
<img src="jim.jpg">
<span>Jim</span>
</div>
<p class="post-date">Today</p>
<h3 class="post-title"><em><strong>Trying to beat the Gold Challenge</strong></em></h3>
<div class="post-content">
<p>I think I <em>nailed</em> the gold challenge for this test.</p>
</div>
</div>
</div>
</div>
<div id="footer">
<div class="container">
<div class="column">
<h4>My Links</h4>
<p>
<a href="">Facebook</a><br>
<a href="">Instagram</a>
</p>
</div>
<div class="column">
<h4>My Story</h4>
<p>Hi There! I am an aspiring web developer.</p>
</div>
</div>
</div>
</body>
</html>nth-child选择器选择共同父级的子项。由于您的两个post-containerdiv 不是同胞姐妹，因此nth-child计数器永远不会达到 2(第一个偶数(。最简单的解决方案是针对#contentdiv，因为它们是同级，但是您的标记存在问题，因为您重用了contentid(id必须是唯一的！我已经将div 更改为具有content类而不是id，并相应地修改了 css。现在，第二篇帖子具有灰色背景，如愿以偿：
.content:nth-child(even) {
background-color: #f2f2f2;
}<!DOCTYPE html>
<html>
<head>
<title> My Blog </title>
<link rel="stylesheet" type="text/css" href="styles.css">
</head>
<body>
<div id="header">
<div class="container">
<a id="header-title" href="index.html">My Blog</a>
<ul id="header-nav">
<li><a href="about.html">About Me</a></li>
<li><a href="mailto:a@yahoo.com">Email Me</a></li>
</ul>
</div>
</div>
<div class="content">
<div class="post-container">
<div class="post">
<div class="post-author">
<img src="aj1.jpg">
<span>Me</span>
</div>
<p class="post-date">Today</p>
<h3 class="post-title"><em><strong>First Decent Looking Webpage</strong></em></h3>
<div class="post-content">
<p>This is all a test to see if everything is coming out ok.</p>
<p>Just more random text to see how it all turns out</p>
<p>Click <a href="https://www.youtube.com">here</a> for my favorite website!</p>
</div>
</div>
</div>
</div>
<div class="content">
<div class="post-container">
<div class="post">
<div class="post-author">
<img src="jim.jpg">
<span>Jim</span>
</div>
<p class="post-date">Today</p>
<h3 class="post-title"><em><strong>Trying to beat the Gold Challenge</strong></em></h3>
<div class="post-content">
<p>I think I <em>nailed</em> the gold challenge for this test.</p>
</div>
</div>
</div>
</div>
<div id="footer">
<div class="container">
<div class="column">
<h4>My Links</h4>
<p>
<a href="">Facebook</a><br>
<a href="">Instagram</a>
</p>
</div>
<div class="column">
<h4>My Story</h4>
<p>Hi There! I am an aspiring web developer.</p>
</div>
</div>
</div>
</body>
</html>