设置网页自适应最大最小宽度，超过则隐藏

#chat{
    width:100%;
min-width:500px;
width:expression_r(document.body.clientWidth < 1000 ? "1000px": "auto" );

    bottom: 1px;
    /* auto;*/
    height:auto;
    overflow:hidden;
    margin-left: auto;
    margin-right: auto;
    background:#8FBAE5;
    text-align:center;
}