#loader {
    display: none;
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: gray;
    opacity: 0.7;
    z-index: 9999;
    text-align: center;
}

#loader:before {
    content: "";
    display: inline-block;
    vertical-align: middle;
    height: 100%;
}

#loader img {
    width: 100px;
    margin: 0 auto;
    display: inline-block;
    vertical-align: middle;
}