12-2 上課範例：style.css

body {
    background-color: #000000;
    margin: 0px;
    padding: 0px;
    background-image: url(images/bg.png);
    background-repeat: no-repeat;
    background-position: center top;
}
#page {
    width:980px;
    margin-top: 250px;
    margin-right: auto;
    margin-left: auto;
    background-color: #000000;
    filter:alpha(opacity=80);
    -moz-opacity:0.8;
    opacity: 0.8;
}