/* 值越大，越不透明*/
img {
opacity: .75; /* Standard: FF gt 1.5, Opera, Safari */
filter: alpha(opacity=75); /* IE lt 8 */
-ms-filter: "alpha(opacity=75)"; /* IE 8 */
-khtml-opacity: .75; /* Safari 1.x */
-moz-opacity: .75; /* FF lt 1.5, Netscape */
}
