SOURCE

document.write('<div class="page-mask"><div class="txt">网站维护中...</div></div>')

if (window.stop)
    window.stop();
else
    document.execCommand("Stop");

 .page-mask {
     position: fixed;
     top: 0;
     left: 0;
     width: 100%;
     height: 100%;
     z-index: 1000;
     background: url(__IMG__/bl-bg.jpg) no-repeat center;
     background-size: cover;
 }
 
 .page-mask .txt {
     font-size: 24px;
     color: #fff;
     position: absolute;
     top: 50%;
     left: 50%;
     transform: translate(-50%, -50%);
 }