滤镜
div.transp { /* make the div translucent */
opacity: 0.6; /* Firefox, Safari(WebKit), Opera)
filter: "alpha(opacity=60)"; /* IE 8 */
filter: alpha(opacity=60); /* IE 4-7 */
zoom: 1; /* needed in IE up to version 7, or set width or height to trigger "hasLayout" */
}