.processMessage {
    text-align: center;
    background: url(../img/wait.gif) no-repeat center #fff;
    z-index: 1000;
    position: fixed; /* or absolute */
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    width:600px;
    height: 450px;
    margin:0 auto;
    border-radius: 7px;
    border: 1px solid black;
}