Why can't I use background image and gradient together?

Question

Hi I want to use background as half page image and half page gradient effect with css. i am doing it here i give you css code and html code but it is not working .

HTML

<div class="inner-pp-15">
    Here I am using image
</div>

CSS

.party-page-15 {
    padding: 20px;
    margin:  0px;
    height:  100%;
    width:   100%;
    background-image: url('../img/party-page.jpg') cover    ;
    background: -moz-linear-gradient(left, rgba(158,0,89,1) 0%, rgba(226,93,168,0) 100%); /* FF3.6+ */
    background: -webkit-gradient(linear, left top, right top, color-stop(0%,rgba(158,0,89,1)), color-stop(100%,rgba(226,93,168,0))); /* Chrome,Safari4+ */
    background: -webkit-linear-gradient(left, rgba(158,0,89,1) 0%,rgba(226,93,168,0) 100%); /* Chrome10+,Safari5.1+ */
    background: -o-linear-gradient(left, rgba(158,0,89,1) 0%,rgba(226,93,168,0) 100%); /* Opera 11.10+ */
    background: -ms-linear-gradient(left, rgba(158,0,89,1) 0%,rgba(226,93,168,0) 100%); /* IE10+ */
    background: linear-gradient(to right, rgba(158,0,89,1) 0%,rgba(226,93,168,0) 100%); /* W3C */
    filter: progid:DXImageTransform.Microsoft.gradient( startColorstr='#9e0059', endColorstr='#00e25da8',GradientType=1 ); /* IE6-9 */
}

How it is possible?