#overlay {
    background: rgba(169, 169, 169, 0.7);
    position: absolute;
    top: 0;
    left: 0;
    height: 100%;
    width: 100%;
}

#loader {
    border: 4px solid #f3f3f3; /* Light grey */
    border-top-color: #999;
    border-radius: 50%;
    width: 60px;
    height: 60px;
    animation: spin 2s linear infinite;
    z-index: 20;
    position: absolute;
    top: 50%;
    left: 50%;
    right: 0;
    bottom: 0;
}

@keyframes spin {
    0% {
        transform: rotate(0deg);
    }
    100% {
        transform: rotate(360deg);
    }
}