<!DOCTYPE html><html> ???<head> ???????<meta charset="UTF-8"> ???????<title></title> ???</head> ???<style> ???????#super{ ???????????width: 200px; ???????????height: 200px; ???????????background: red; ???????????display: flex; ???????????align-items: center; ???????????justify-content: center; ???????} ???????#sub{ ???????????width: 100px; ???????????height: 100px; ???????????background: blue; ???????} ???</style> ???<body> ???????<div id="super"> ???????????<div id="sub"></div> ???????</div> ???</body></html>只要在父元素放上display:flex(flex布局)
align-items:center 垂直居中
justify-content:center 垂直居中
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css水平垂直居中
原文地址：https://www.cnblogs.com/GeekXwj/p/9304504.html