滚动区块的透明度渐变(遮罩)

闲话不说，先看效果：

代码实现：

<div class="rollingBlock">
    <div class="mask"></div>
    <ul class="list">
        <li>01</li>
        <li>02</li>
        <li>03</li>
        <li>04</li>
        <li>05</li>
        <li>06</li>
        <li>07</li>
        <li>08</li>
        <li>09</li>
        <li>10</li>
    </ul>
</div>

div.rollingBlock{
    position: relative;
    box-sizing: border-box;
    width: 800px;
    height: 600px;
    background-color: #021019;  
    border-radius: 2px;
    overflow: hidden;
    transition: background-color  0.5s;
    -webkit-transition: background-color 0.5s;
    -moz-transition: background-color 0.5s;
    -o-transition: background-color 0.5s;
    -ms-transition: background-color 0.5s; 
}
div.rollingBlock div.mask{
    position: absolute;
    z-index:999;
    top: 0;
    left: 0;
    box-sizing: border-box;
    width: 100%;
    height: 100%;
    background: -webkit-gradient(linear, 0 0, 0 100%, from(rgba(2,16,25,1)), to(rgba(2,16,25,0)));
    background: -moz-linear-gradient(top, rgba(0,0,0, 1), rgba(255, 255, 255, 0));
    background: -o-linear-gradient(top,  rgba(0,0,0, 1), rgba(255, 255, 255, 0));
    background: -ms-linear-gradient(top,  rgba(0,0,0, 1), rgba(255, 255, 255, 0));
    background: linear-gradient(top,  rgba(0,0,0, 1), rgba(255, 255, 255, 0));
}
div.rollingBlock div.mask:hover{
    background: transparent;
}
div.rollingBlock ul{
    position: absolute;
    left: 22px;
    top: 0;
    width: 100%;
}
div.rollingBlock li{
    box-sizing: border-box;
    width: 100%;
    height: 40px;
　　 text-align: center;
    padding: 0 10px 0 1px;
    margin-top: 6px;
    line-height: 40px;
    background-color: rgba(0,0,0,0.5);
    border-radius: 2px;
}

$("div.rollingBlock").hover(function(){
    clearInterval(time);
}, function() {
    roll();
});
var time = null;
var control = false;
function roll() {
    clearInterval(time);
    time = setInterval(function() {
        // var top = Number.parseInt(getStyle(oUl, 'top'));
        var top = ul.position().top;
        ul.animate({top:top-46 + 'px'}, "slow",function() {
            top = Number.parseInt(getStyle(oUl, 'top'));
            var obj = ul.children().first().remove();
            ul.append(obj);
            ul.css("top",top+46 + 'px');
        } );
    }, 2000);
}
roll();

 注意遮罩的rgba()色彩要与盒子的背景色一致