<!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <title></title> <style type="text/css"> #box{ margin: 0 auto; width: 150px; height: 150px; border: 1px solid #FF0000; position: relative; }
#box #text{ width: 50px; height: 50px; position: absolute; left: 0; right: 0; top: 0; bottom: 0; margin: auto; } </style> </head> <body> <div id="box"> <div id="text"> 123 </div> </div> </body> </html>
left:0; right:0; top:0; bottom:0; margin：auto;会使text居中，如果text没有宽高，则会继承父集的宽高。适合body 内的遮罩，