How covered the entire screen has been centered and
<! DOCTYPE HTML > < HTML lang = "EN" > < head > < Meta charset = "UTF-. 8" > < style > * { margin : 0 ; padding : 0 ; } .c1 { / * width: 100%; * / / * height: 100px; * / background-Color : Red ; position : Fixed ; /*position: fixed;*/ top: 0; right: 0; left: 0; bottom: 0; } .c2{ width: 600px; height: 400px; background-color: white; position: fixed; top: 50%; left: 50%; margin-top:-200px; margin-left:-300px; } </style> <title>工会公告</title> </head> <body> <div class="c1"></div> <div class="c2"></div> <!--<p>sdd</p>--> </body> </html>