问IE8选择指针的梯度没有显示

EN

<label class="myselect">
    <select class="date">
        <option value="y">Show Year</option>
        <option value="m" selected="selected">Show Month</option>
    </select>
</label>

select {
    height: 30px;
    border: 1px solid black;
    width: auto !important;
    padding: 3px;
    margin: 0;
    line-height: 30px;
}
.myselect {
    position: relative;
    display: inline-block;
}
select, .myselect:before {
    background: #ffffff;
    /* Old browsers */
    /* IE9 SVG, needs conditional override of 'filter' to 'none' */
    background: url(data:image/svg+xml;
    base64, 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);
    background: -moz-linear-gradient(top, #ffffff 0%, #eeeeee 100%);
    /* FF3.6+ */
    background: -webkit-gradient(linear, left top, left bottom, color-stop(0%, #ffffff), color-stop(100%, #eeeeee));
    /* Chrome,Safari4+ */
    background: -webkit-linear-gradient(top, #ffffff 0%, #eeeeee 100%);
    /* Chrome10+,Safari5.1+ */
    background: -o-linear-gradient(top, #ffffff 0%, #eeeeee 100%);
    /* Opera 11.10+ */
    background: -ms-linear-gradient(top, #ffffff 0%, #eeeeee 100%);
    /* IE10+ */
    background: linear-gradient(to bottom, #ffffff 0%, #eeeeee 100%);
    /* W3C */
    filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='#ffffff', endColorstr='#eeeeee', GradientType=0);
    /* IE6-8 */
    -webkit-border-radius: 6px;
    -moz-border-radius: 6px;
    border-radius: 6px;
}
.myselect:before {
    content:"";
    height: 41px;
    right: 2px;
    top: 2px;
    width: 21px;
    display: block;
    position: absolute;
}
.myselect:after {
    top: 20px;
    content:'';
    right: 8px;
    position: absolute;
    pointer-events: none;
    width: 0;
    height: 0;
    border-left: 5px solid transparent;
    border-right: 5px solid transparent;
    border-top: 5px solid black;
}
/*and in my explorer 8 stylesheet i have*/
 select {
    position: relative;
    z-index: 1;
    filter: none !important;
    background: #FFFFFF;
    background: -webkit-gradient(linear, 0 0, 0 bottom, from(#FFFFFF), to(#EEEEEE));
    background: -webkit-linear-gradient(#FFFFFF, #EEEEEE);
    background: -moz-linear-gradient(#FFFFFF, #EEEEEE);
    background: -ms-linear-gradient(#FFFFFF, #EEEEEE);
    background: -o-linear-gradient(#FFFFFF, #EEEEEE);
    background: linear-gradient(#FFFFFF, #EEEEEE);
    -pie-background: linear-gradient(#FFFFFF, #EEEEEE);
    behavior: url("/css/PIE.htc");
}
.myselect:before {
    background: #FFFFFF;
    background: -webkit-gradient(linear, 0 0, 0 bottom, from(#FFFFFF), to(#EEEEEE));
    background: -webkit-linear-gradient(#FFFFFF, #EEEEEE);
    background: -moz-linear-gradient(#FFFFFF, #EEEEEE);
    background: -ms-linear-gradient(#FFFFFF, #EEEEEE);
    background: -o-linear-gradient(#FFFFFF, #EEEEEE);
    background: linear-gradient(#FFFFFF, #EEEEEE);
    -pie-background: linear-gradient(#FFFFFF, #EEEEEE);
    behavior: url("/css/PIE.htc");
}