- 水平居中
- inline 元素：
text-align: center
- block 元素：
margin: auto
- absolute 元素：
left: 50% + margin-left 负值
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<meta http-equiv="X-UA-Compatible" content="ie=edge" />
<title>水平对齐</title>
<style type="text/css">
.container {
border: 1px solid #ccc;
margin: 10px;
padding: 10px;
}
.item {
background-color: #ccc;
}
.container-1 {
text-align: center;
}
.container-2 .item {
width: 500px;
margin: auto;
}
.container-3 {
position: relative;
height: 100px;
}
.container-3 .item {
width: 300px;
height: 100px;
position: absolute;
left: 50%;
margin-left: -150px;
}
</style>
</head>
<body>
<div class="container container-1">
<span>一段文字</span>
</div>
<div class="container container-2">
<div class="item">this is block item</div>
</div>
<div class="container container-3">
<div class="item">this is absolute item</div>
</div>
</body>
</html>
- 垂直居中
- inline 元素：line-height 的值等于 height 值
- absolute 元素：top: 50% + margin-top 负值
- absolute 元素：`transform: translate(-50%,-50%)`
- absolute 元素：top,left,bottom,right = 0 + margin: auto
```html
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<meta http-equiv="X-UA-Compatible" content="ie=edge" />
<title>垂直对齐</title>
<style type="text/css">
.container {
border: 1px solid #ccc;
margin: 10px;
padding: 10px;
height: 200px;
}
.item {
background-color: #ccc;
}
.container-1 {
text-align: center;
line-height: 200px;
height: 200px;
}
.container-2 {
position: relative;
}
.container-2 .item {
width: 300px;
height: 100px;
position: absolute;
left: 50%;
margin-left: -150px;
top: 50%;
margin-top: -50px;
}
.container-3 {
position: relative;
}
.container-3 .item {
width: 200px;
height: 80px;
position: absolute;
left: 50%;
top: 50%;
transform: translate(-50%, -50%);
}
.container-4 {
position: relative;
}
.container-4 .item {
width: 100px;
height: 50px;
position: absolute;
top: 0;
left: 0;
bottom: 0;
right: 0;
margin: auto;
}
</style>
</head>
<body>
<div class="container container-1">
<span>一段文字</span>
</div>
<div class="container container-2">
<div class="item">this is item</div>
</div>
<div class="container container-3">
<div class="item">this is item</div>
</div>
<div class="container container-4">
<div class="item">this is item</div>
</div>
</body>
</html>
```