demo地址:http://codepen.io/tianzi77/pen/gpEMxb
僞元素能做什麼呢?
“僞元素”,顧名思義。它創建了一個虛假的元素,並插入到目標元素內容之前或之後。
單詞“pseudo”是希臘語的英譯,它的基本意思是“說謊的,不誠實的,錯誤的。”因此叫僞元素是適合的。因爲在文檔中它不實際改變什麼。相反的,它們是像幽靈一般的元素插入在css中,他們對用戶是可見的,可以通過css控制。
基本語法
:before 和 :after 僞元素編碼非常簡單(和大多數的css屬性一樣不需要一大堆的前綴)。這裏是一個簡單的例子。
#example:before {
content: "#";
}
#example:after {
content: ".";
}
在看一個列子
<a href="" class="tianzi">ddd</a>
a.tianzi{
position: relative}
a.tianzi:after {
/*
position: absolute;
left: 0;
top: 0;
*/
content: "";
/* width: 100%;*/
height: 2px;
border: 1px solid red;
/* margin-top: -2px;*/
background: red;
}
這樣就會出現
這樣的效果。
爲了出現demo的效果。我們需要對僞元素就行定位。
ps:僞元素插入默認是行內元素。
下面看看demo的代碼:
<nav class="main-nav" id="main-nav">
<a href="/" class="home">
Blog
</a>
<a href="/video-screencasts/" class="videos">
Videos
</a>
<a href="/almanac/" class="almanac">
Almanac
</a>
<a href="/snippets/" class="snippets">
Snippets
</a>
<a href="/forums/" class="forums">
Forums
</a>
<a href="/jobs/" class="jobs">
Jobs
</a>
<a href="/lodge/" class="lodge">
Lodge
</a>
</nav>
關鍵在於樣式:
body {
background-color: #abcdef;
}
.main-nav {
display: flex;
}
.main-nav>a {
padding: 15px;
color: white;
position: relative;
display: inline-block;
text-decoration: none;
transition: all .3s ease-out;
}
.main-nav>a.home::before,
.main-nav>a.home:hover,
.main-nav>a.home:active,
body.home .main-nav>a.home {
background: #e18728;
color: lightpink;
}
.main-nav>a.home::before {
position: absolute;
left: 0;
top: 0;
content: "";
width: 100%;
height: 2px;
margin-top: -2px;
}
.main-nav>a.videos::before,
.main-nav>a.videos:hover,
.main-nav>a.videos:active,
body.page-template-video-archive-php .main-nav>a.videos,
body.page-template-video-single-php .main-nav>a.videos {
background: #BE4C39;
}
.main-nav>a::before {
content: "";
position: absolute;
top: 0;
left: 0;
margin-top: -2px;
height: 2px;
width: 100%;
}
.main-nav>a.almanac::before,
.main-nav>a.almanac:hover,
.main-nav>a.almanac:active,
body.page-template-page-almanac-group-php .main-nav>a.almanac,
body.page-template-page-almanac-single-php .main-nav>a.almanac {
background: #9351A6;
}
.main-nav>a.snippets::before,
.main-nav>a.snippets:hover,
.main-nav>a.snippets:active,
body.page-template-page-snippet-cat-php .main-nav>a.snippets,
body.page-template-page-snippet-php .main-nav>a.snippets {
background: #4472B9;
}
.main-nav>a.forums::before,
.main-nav>a.forums:hover,
.main-nav>a.forums:active,
body.bbpress .main-nav>a.forums {
background: #4CA454;
}
.main-nav>a.jobs::before,
.main-nav>a.jobs:hover,
.main-nav>a.jobs:active,
body.page-template-jobs-php .main-nav>a.jobs {
background: #d49b00;
}
.main-nav>a.lodge::before,
.main-nav>a.lodge:hover,
.main-nav>a.lodge:active,
body.page-template-page-lodge-php .main-nav>a.lodge,
body.page-template-lodge-signup-php .main-nav>a.lodge,
body.page-template-page-lodge-group-php .main-nav>a.lodge,
body.page-template-lodge-video-php .main-nav>a.lodge {
background: #444444;
}