Question

我的问题是关于w3school关于响应式网格设计的一个例子。

<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<style>
* {
    box-sizing: border-box;
}
.row::after {
    content: "";
    clear: both;
    display: table;
}
[class*="col-"] {
    float: left;
    padding: 15px;
}
html {
    font-family: "Lucida Sans", sans-serif;
}
.header {
    background-color: #9933cc;
    color: #ffffff;
    padding: 15px;
}
.menu ul {
    list-style-type: none;
    margin: 0;
    padding: 0;
}
.menu li {
    padding: 8px;
    margin-bottom: 7px;
    background-color: #33b5e5;
    color: #ffffff;
    box-shadow: 0 1px 3px rgba(0,0,0,0.12), 0 1px 2px rgba(0,0,0,0.24);
}
.menu li:hover {
    background-color: #0099cc;
}
.aside {
    background-color: #33b5e5;
    padding: 15px;
    color: #ffffff;
    text-align: center;
    font-size: 14px;
    box-shadow: 0 1px 3px rgba(0,0,0,0.12), 0 1px 2px rgba(0,0,0,0.24);
}
.footer {
    background-color: #0099cc;
    color: #ffffff;
    text-align: center;
    font-size: 12px;
    padding: 15px;
}
/* For mobile phones: */
[class*="col-"] {
    width: 100%;
}
@media only screen and (min-width: 768px) {
    /* For desktop: */
    .col-1 {width: 8.33%;}
    .col-2 {width: 16.66%;}
    .col-3 {width: 25%;}
    .col-4 {width: 33.33%;}
    .col-5 {width: 41.66%;}
    .col-6 {width: 50%;}
    .col-7 {width: 58.33%;}
    .col-8 {width: 66.66%;}
    .col-9 {width: 75%;}
    .col-10 {width: 83.33%;}
    .col-11 {width: 91.66%;}
    .col-12 {width: 100%;}
}
</style>
</head>
<body>

<div class="header">
  <h1>Chania</h1>
</div>

<div class="row">

<div class="col-3 menu">
  <ul>
    <li>The Flight</li>
    <li>The City</li>
    <li>The Island</li>
    <li>The Food</li>
  </ul>
</div>

<div class="col-6">
  <h1>The City</h1>
  <p>Chania is the capital of the Chania region on the island of Crete. The city can be divided in two parts, the old town and the modern city.</p>
</div>

<div class="col-3 right">
  <div class="aside">
    <h2>What?</h2>
    <p>Chania is a city on the island of Crete.</p>
    <h2>Where?</h2>
    <p>Crete is a Greek island in the Mediterranean Sea.</p>
    <h2>How?</h2>
    <p>You can reach Chania airport from all over Europe.</p>
  </div>
</div>

</div>

<div class="footer">
  <p>Resize the browser window to see how the content respond to the resizing.</p>
</div>

</body>
</html>

在此示例中，它使用.row::after分隔row和footer。如果我取消row的伪元素，footer的背景将扩展到整行。我想知道为什么会这样？从我所学到的row和footer都是display:block，它们不应该叠加在一起吗？如果不使用伪元素，为什么footer的背景会扩展？

Answer 1

伪元素用于清除.row中包含的浮点数。它被称为 clearfix 。

没有明确修复：

＆＃13;

.row::after {
    content: "";
    clear: both;
    display: table;
}

.col-md-6 {
  float: left;
  width: 50%;
}

.row-color {
  background-color: gold;
}

＆＃13;

<div class="row-color">
  <div class="col-md-6">
    Left
  </div>
  <div class="col-md-6">
    Right
  </div>
</div>

＆＃13;

使用clearfix：

＆＃13;

.row::after {
    content: "";
    clear: both;
    display: table;
}

.col-md-6 {
  float: left;
  width: 50%;
}

.row-color {
  background-color: gold;
}

＆＃13;

<div class="row row-color">
  <div class="col-md-6">
    Left
  </div>
  <div class="col-md-6">
    Right
  </div>
</div>

＆＃13;

为什么使用伪元素来分隔块元素？

1 个答案: