<script>

var bodyBgs = [];

bodyBgs[0]=    " https://new-service.biliapi.net/picture/chatres/102d1b48515346ec8e9fb543b54ec454acgpic-197.jpg  "    ;
bodyBgs[1]=    " https://new-service.biliapi.net/picture/chatres/102d1b48515346ec8e9fb543b54ec454acgpic-61.jpg  "    ;
bodyBgs[2]=    " https://tva1.sinaimg.cn/large/9bd9b167gy1g4lhdxdmbuj21hc0xcakc.jpg  "    ;
bodyBgs[3]=    " https://tva3.sinaimg.cn/large/9bd9b167gy1fwsgda81zhj21hc0u0b29.jpg  "    ;


 var randomBgIndex = Math.round( Math.random() * 4 );

 document.write('<style>body{background:url(' + bodyBgs[randomBgIndex] + ') no-repeat 50% 0}</style>');

</script>