Use CSS to center div horizontally and vertically

There are many solutions to achieve centering. Here we introduce the solution of pure CSS using absolute with margin.

1. p width and height are fixed

width: 400px;
height: 200px;
position: absolute;
top: 50%;
left: 50%;
margin-top: -100px;
margin-left: -200px;

margin-top is -(height / 2), margin-left is -(width / 2). Of course, you can not use margin, that is, top is calc(100% - height) / 2, left is calc(100% - width) / 2, but it is recommended not to use calc() if you don't need it.

2. pThe width and height are not fixed

width: 50%;
height: 50%;
position: absolute;
top: 0;
right: 0;
bottom: 0;
left: 0;
margin: auto;

Note that this applies to situations where the width and height need to be specified, such as using percentages or using js Modify dynamically, otherwise it may be treated as 100%.

You can also use translate() without margin, as follows:

width: 50%;
height: 50%;
position: absolute;
top: 50%;
left: 50%;
transform: translateX(-50%) translateY(-50%);

3. CSS3 variable width, horizontal and vertical centering

justify-content: center; /* 子元素水平居中 */
align-items: center;     /* 子元素垂直居中 */
display: -webkit-flex;

in the parent element Add it to achieve horizontal and vertical centering of child elements.

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