1.居中一个浮动元素，父元素和子元素同时左浮动，然后父元素相对左移动50%，子元素相对右移动50%，或者子元素相对左移动-50%

<div class="p">
    <div class="c">
        <span>水平居中浮动元素</span>
    </div>
</div>

.p {
    position: relative;
    float: left;
    left: 50%;
}

.c {
    position: relative;
    float: left;
    right: 50%;
}

2.垂直水平居中

<div class="center">
    <span>水平垂直居中</span>
</div>

.center {
    position: absolute;
    width: 200px;
    height: 100px;
    left: 50%;
    top: 50%;
    margin-top: -50px;
    margin-left: -100px;
}

3.图片水平垂直居中tabel_cell

<div class="test_box">
    <img src="img/head.png" alt="">
</div>

.test_box {
    width: 200px;
    height: 200px;
    position: absolute;
    top: 50%;
    left: 50%;
    margin-top: -100px;
    margin-left: -100px;
    border: 1px solid #000;
}

.test_box img {
    margin: auto;
    position: absolute;
    right: 0;
    bottom: 0;
    left: 0;
    top: 0;
}

4.图片水平垂直居中span

<div class="test_box">
    <span class="hook"></span>
    <img src="img/book.jpg" alt="">
</div>

.test_box {
    width: 200px;
    height: 200px;
    text-align: center;
    border: 1px solid #000;
    position: absolute;
    left: 50%;
    top: 50%;
    margin-left: -100px;
    margin-top: -100px;
}

.test_box .hook {
    display: inline-block;
    height: 100%;
    margin-left: -1px;
    vertical-align: middle;
}

.test_box img {
    vertical-align: middle;
}

5.水平垂直居中（适用于父级元素只有一个子元素的情况，比如全屏的效果）

<div class="outer">
    <h1 class="inner">适用于父级元素只有一个子元素的情况，比如全屏的效果。</h1>
</div>

.outer {
    position: absolute;
    width: 400px;
    height: 400px;
    background: #f80;
    top: 50%;
    left: 50%;
    margin-top: -200px;
    margin-left: -200px;
}

.inner {
    border: 3px solid green;
    position: absolute;
    margin: auto;
    overflow: hidden;
    width: 50%;
    height: 50%;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
}

6.水平垂直居中（方法一、使用 line-height）

<div class="box">
    <div class="content">水平垂直居中</div>
</div>

.box {
    width: 200px;
    height: 200px;
    margin: 0 auto;
    background: #ddf;
    position: absolute;
    top: 50%;
    left: 50%;
    margin-top: -100px;
    margin-left: -100px;
}

.content {
    line-height: 200px;
    vertical-align: middle;
    text-align: center;
    overflow: hidden;
}

7.水平垂直居中（方法二、把容器当作表格单元）

<div class="box">
    <div class="content">水平垂直居中</div>
</div>

.box {
    width: 200px;
    height: 200px;
    background: #ddf;
    display: table;
    position: absolute;
    top: 50%;
    left: 50%;
    margin-top: -100px;
    margin-left: -100px;
}

.content {
    display: table-cell;
    vertical-align: middle;
    text-align: center;
}

8.水平垂直居中（方法三、IE6下的解决方案）

<div class="box">
    <div class="content">水平垂直居中</div>
</div>

.box {
    width: 200px;
    height: 200px;
    background: #ddf;
    display: table;
    position: absolute;
    top: 50%;
    left: 50%;
    margin-top: -100px;
    margin-left: -100px;
}

.content {
    _position: relative;
    _top: 50%;
    display: table-cell;
    vertical-align: middle;
    text-align: center;
}

.content > div {
    _position: relative;
    _top: -50%;
}

9.水平垂直居中（方法四、负边距margin的使用）

<div class="box">
    <div class="content">水平垂直居中</div>
</div>

.box {
    width: 200px;
    height: 200px;
    background: #ddf;
    display: table;
    position: absolute;
    top: 50%;
    left: 50%;
    margin-top: -100px;
    margin-left: -100px;
}

.content {
    width: 100px;
    height: 80px;
    padding: 10px;
    background: #abc;
    position: absolute;
    top: 50%;
    left: 50%;
    margin-left: -60px;
    margin-top: -50px;
}

.content > div {
    _position: relative;
    _top: -50%;
}