position 元素已知宽度
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>水平垂直居中</title>
<style>
.father{
background-color: #FF8C00;
width: 600px;
height:600px;
position: relative;
}
.child{
background-color: rosybrown;
width: 300px;
height: 300px;
position: absolute;
left: 50%;
top: 50%;
margin: -150px 0 0 -150px;
}
</style>
</head>
<body>
<div class="father">
<div class="child">
hello word!!!
</div>
</div>
</body>
</html>
position 元素未知宽度
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>水平垂直居中</title>
<style>
.father{
background-color: #FF8C00;
height: 300px;
position: relative;
}
.child{
background-color: #F00;
width: 100px;
height: 100px;
position: absolute;
left: 50%;
top: 50%;
transform: translate(-50%,-50%)
}
</style>
</head>
<body>
<div class="father">
<div class="child">
hello word!!!
</div>
</div>
</body>
</html>
position 可以不知道宽
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>水平垂直居中</title>
<style>
.father{
background-color: #FF8C00;
height: 500px;
width: 500px;
position: relative;
}
.child{
background-color: #F00;
width: 200px;
height: 200px;
position:absolute;
left:0;
top: 0;
bottom: 0;
right: 0;
margin: auto;
}
</style>
</head>
<body>
<div class="father">
<div class="child">
hello word!!!
</div>
</div>
</body>
</html>
flex可以不知道宽
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>水平垂直居中</title>
<style>
.father{
background-color: #FF8C00;
height: 500px;
width: 500px;
display: flex;/*flex布局*/
justify-content: center;/*使子项目水平居中*/
align-items: center;/*使子项目垂直居中*/
}
.child{
background-color: #F00;
width: 200px;
height: 200px; }
</style>
</head>
<body>
<div class="father">
<div class="child">
hello word!!!
</div>
</div>
</body>
</html>
table-cell布局 需要三个标签 相对麻烦 因为table-cell相当与表格的td，td为行内元素，无法设置宽和高，所以嵌套一层，嵌套一层必须设置display: inline-block;td的背景覆盖了橘黄色，不推荐使用
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>水平垂直居中</title>
<style>
.father{
background-color: #FF8C00;
height: 500px;
width: 500px;
display: table;
}
.child{
background-color: #F00;
width: 200px;
height: 200px;
display: table-cell;
vertical-align: middle;/*使子元素垂直居中*/
text-align: center;/*使子元素水平居中*/
}
.childInner{
background-color: #;
display: inline-block;/*使子元素呈现块状*/
width: 100px;
height: 100px;
}
</style>
</head>
<body>
<div class="father">
<div class="child">
<div class="childInner"> hello word!!!</div>
</div>
</div>
</body>
</html>