How to style input type file element

index.html

<div class="fileUpload btn btn-primary">
    <span>Upload</span>
    <input type="file" class="upload" />
</div>

style.css

.fileUpload {
    background: #ff4001 none repeat scroll 0 0;
    border-radius: 0;
    font-weight: 700;
    margin: 0;
    overflow: hidden;
    position: relative;
    width: 90px;
}
.fileUpload input.upload {
    position: absolute;
    top: 0;
    right: 0;
    margin: 0;
    padding: 0;
    font-size: 20px;
    cursor: pointer;
    opacity: 0;
    filter: alpha(opacity=0);
}