如何实现CSS居中？–CSS居中常用方法

来源：http://www.ido321.com/824.html

一、水平居中

      1、内联元素居中：相对父级块级元素居中对齐

.center-children {
  text-align: center;
}

 

      2、块级元素居中：设置margin-left和margin-right为auto让它居中（同时还要设置width，否则它就会承满整个容器，无法看出居中效果）

.center-me {
  margin: 0 auto;
}

 

如果有很多块级元素需要水平居中成一行，最好使用一个不同的display类型。这是一个使用inline-block和flex的例子。

演示地址：http://jsfiddle.net/Web_Code/5fvrwwk1/embedded/result/

<main class="inline-block-center">
  <div>
    I'm an element that is block-like with my siblings and we're centered in a row.
  </div>
  <div>
    I'm an element that is block-like with my siblings and we're centered in a row. I have more content in me than my siblings do.
  </div>
  <div>
    I'm an element that is block-like with my siblings and we're centered in a row.
  </div>
</main>
<main class="flex-center">
  <div>
    I'm an element that is block-like with my siblings and we're centered in a row.
  </div>
  <div>
    I'm an element that is block-like with my siblings and we're centered in a row. I have more content in me than my siblings do.
  </div>
  <div>
    I'm an element that is block-like with my siblings and we're centered in a row.
  </div>
</main>

css:

body {
  background: #f06d06;
  font-size: 80%;
}
main {
  background: white;
  margin: 20px 0;
  padding: 10px;
}
main div {
  background: black;
  color: white;
  padding: 15px;
  max-width: 125px;
  margin: 5px;
}
.inline-block-center {
  text-align: center;
}
.inline-block-center div {
  display: inline-block;
  text-align: left;
}
.flex-center {
  display: flex;
  justify-content: center;
}

二、垂直居中

       1、内联元素：设置相等的上下padding，或者利用line-height

.link {
  padding-top: 30px;
  padding-bottom: 30px;
}

文本不会换行的情况下，可以使用line-height，让其与height相等去对齐文本。

.center-text-trick {
  height: 100px;
  line-height: 100px;
  white-space: nowrap;
}

 

多行的文本也可以利用上下等padding的方式也可以让多行居中，但是如果这方法没用，你可以让这些文字的容器按table cell模式显示，然后设置文字的vertical-align属性对齐，

演示地址：http://jsfiddle.net/Web_Code/5fvrwwk1/1/embedded/result/

html:

<table>
  <tr>
    <td>
      I'm vertically centered multiple lines of text in a real table cell.
    </td>
  </tr>
</table>
<div class="center-table">
  <p>I'm vertically centered multiple lines of text in a CSS-created table layout.</p>
</div>

css

body {
  background: #f06d06;
  font-size: 80%;
}
table {
  background: white;
  width: 240px;
  border-collapse: separate;
  margin: 20px;
  height: 250px;
}
table td {
  background: black;
  color: white;
  padding: 20px;
  border: 10px solid white;
  /* default is vertical-align: middle; */
}
.center-table {
  display: table;
  height: 250px;
  background: white;
  width: 240px;
  margin: 20px;
}
.center-table p {
  display: table-cell;
  margin: 0;
  background: black;
  color: white;
  padding: 20px;
  border: 10px solid white;
  vertical-align: middle;
}

 

     2、块级元素

若元素有固定高度，可以这样垂直居中

.parent {
  position: relative;
}
.child {
  position: absolute;
  top: 50%;
  height: 100px;
  margin-top: -50px; /* 如果没有使用: border-box; 的盒子模型则需要设置这个 */
}

如果不知道元素高度，则这样

.parent {
  position: relative;
}
.child {
  position: absolute;
  top: 50%;
  transform: translateY(-50%);
}

也可以使用flexbox

<main>
  <div>
     I'm a block-level element with an unknown height, centered vertically within my parent.
  </div>
</main>

body {
  background: #f06d06;
  font-size: 80%;
}
main {
  background: white;
  height: 300px;
  width: 200px;
  padding: 20px;
  margin: 20px;
  display: flex;
  flex-direction: column;
  justify-content: center;
  resize: vertical;
  overflow: auto;
}
main div {
  background: black;
  color: white;
  padding: 20px;
  resize: vertical;
  overflow: auto;
}

 

三、同时水平和垂直居中

      1、元素有固定高度和宽度：先绝对居中，然后上移和左移50%的宽度即可

//这种方案有极好的跨浏览器支持。
.parent {
  position: relative;
}
.child {
  width: 300px;
  height: 100px;
  padding: 20px;
  position: absolute;
  top: 50%;
  left: 50%;
  margin: -70px 0 0 -170px;
}

 

     2、元素的高度和宽度未知或可变的：使用transofrm属性在两个方向都平移负50%

   1: .parent {

   2:   position: relative;

   3: }

   4: .child {

   5:   position: absolute;

   6:   top: 50%;

   7:   left: 50%;

   8:   transform: translate(-50%, -50%);

   9: }