body {
    text-align: center;
}

a::before {
    content: "";

    display: inline-block;
    height: 20px;
    width: 20px;
    margin-right: 10px;
    vertical-align: middle;

    background-image: url(../images/pdf-download.png);
    background-repeat: no-repeat;
    background-attachment: scroll;
    background-position: center;
    background-size: 100% 100%;
}