# before、after
{% hint style="info" %}
### ::before 原本的元素\[之前]加 入內容 ::after 則是原本的元素\[之後]加入內容
{% endhint %}
## 使用說明
* 使用時，需要加上content 才能使用
* 產生出來虛擬元素為inline特性。無法控制寬、高、行距
* 有關SEO內容，不應該放在content內
* content:搜尋引擎找不倒裡面的文字
* 可以減少HTML標籤數量，相對也加重瀏覽器的渲染區塊
## 偽元素
```css
@charset "UTF-8";
.box {
background-color: yellowgreen;
width: 500px;
padding: 15px;
margin-left: auto;
margin-right: auto;
}
.box::before {
content: "我是 before";
background-color: pink;
display: block;
}
.box::after {
content: "我是 after";
background-color: wheat;
display: block;
}
```
### 反轉
{% tabs %}
{% tab title="First Tab" %}
```markup
```
{% endtab %}
{% tab title="Second Tab" %}
```css
@charset "utf-8";
*,
*::before,
*::after {
box-sizing: border-box;
}
.flip .base-text {
float: right;
}
.flip .base-photo {
float: left;
}
.base {
width: 1200px;
margin-left: auto;
margin-right: auto;
}
.base::after {
content: "";
display: block;
clear: both;
}
.base-text,
.base-photo {
width: 50%;
padding: 15px;
}
.base-text {
float: left;
background-color: yellowgreen;
}
.base-photo {
float: right;
background-color: pink;
}
```
{% endtab %}
{% endtabs %}
## 麵包屑
```css
/* @charset "utf-8"; */
/* Base */
* {
box-sizing: border-box;
}
body {
font-family: Arial, Helvetica, "微軟正黑體", sans-serif;
font-size: 15px;
}
.breadcrumb{
margin-top: 20px;
margin-bottom: 20px;
}
.breadcrumb__item a:hover{
color: #2ea3f2;
}
.breadcrumb__item + .breadcrumb__item::before{
content: "»";
margin-right: 3px;
color:#aaa;
}
.breadcrumb__item a{
color: #aaa;
}
```
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