.overlay {
    /* Height & width depends on how you want to reveal the overlay (see JS below) */
    height: 100%;
    width: 100%;
    position: fixed; /* Stay in place */
    z-index: 99; /* Sit on top */
    left: 0;
    top: 0;
    background-color: rgb(0,0,0); /* Black fallback color */
    background-color: rgba(0,0,0, 0.9); /* Black w/opacity */
    overflow-x: hidden; /* Disable horizontal scroll */
    transition: 0.5s; /* 0.5 second transition effect to slide in or slide down the overlay (height or width, depending on reveal) */
}

.overlay-content {
    position: relative;
    top: 25%; /* 25% from the top */
    width: 100%; /* 100% width */
    text-align: center; /* Centered text/links */
    margin-top: 30px; /* 30px top margin to avoid conflict with the close button on smaller screens */
    color: #D3D3D3;
}