Tag Archives: web frontend

CSS: several ways to center the box vertically and horizontally

method 1: width and height known.

idea:
relative positioning of the parent element
absolute positioning of the child element
left: 50%; top: 50%;
margin-left: negative half width.
margin-top: minus half of the height; 

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>居中</title>
    <style type="text/css">
        #box{
            width: 400px;
            height: 200px;
            position: relative;
            background: red;
        }
        #box1{
            width: 200px;
            height: 100px;
            position: absolute;
            top: 50%;
            left: 50%;
            margin-left: -100px;
            margin-top: -50px;
            background: green;
        }
    </style>
</head>
<body>
    <div id="box">
        <div id="box1">

        </div>
    </div>
</body>
</html>

method 2: width and height themselves unknown

means that the subbox itself still has a width and a height that it doesn’t know.
relative positioning of parent box
absolute positioning of child box
top, right, bottom, left all 0
margin: auto; 

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>居中</title>
    <style type="text/css">
        #box{
            width: 800px;
            height: 400px;
            position: relative;
            background: red;
        }
        #box1{
            width: 100px;
            height: 50px;
            position: absolute;
            top: 0;
            right: 0;
            bottom: 0;
            left: 0;
            margin: auto;
            background: green;
        }
    </style>
</head>
<body>
    <div id="box">
        <div id="box1">

        </div>
    </div>
    <script type="text/javascript">

    </script>
</body>
</html>

method 3: flex layout 

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>垂直居中</title>
    <style type="text/css">
        .box{
            width: 400px;
            height: 200px;
            background: #f99;
        }
        .box1{
            width: 200px;
            height: 100px;
            background: green;
        }
        .center{
            display: flex;
            justify-content: center;//实现水平居中
            align-items: center;//实现垂直居中
        }
    </style>
</head>
<body>
    <div class="box center">
        <div class="box1">

        </div>
    </div>
</body>
</html>

Method 4: translation positioning +transform 

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>css3让一个盒子居中</title>
    <style type="text/css">
        .parent_box{
            width: 400px;
            height: 200px;
            background: red;
            position: relative;
        }
        .child_box{
            width: 200px;
            height: 100px;
            background: #9ff;
            position: absolute;
            top: 50%;
            left: 50%;
            transform: translate( -50%,-50%);
        }
    </style>
</head>
<body>
    <div class="parent_box">
        <div class="child_box">

        </div>
    </div>
</body>
</html>

method 5: table-cell layout

parent display: table-cell; vertical-align: middle; Sub-level margin: 0 auto;

** horizontal center

plus a horizontal center: margin-left: 50%; transform: translateX(-50%);