.modal {
    display: none;
    /* Hidden by default */
    position: fixed;
    /* Stay in place */
    z-index: 1;
    /* Sit on top */
    left: 0;
    top: 0;
    width: 100%;
    /* Full width */
    height: 100%;
    /* Full height */
    overflow: auto;
    /* Enable scroll if needed */
    background-color: rgb(0, 0, 0);
    /* Fallback color */
    background-color: rgba(0, 0, 0, 0.4);
    /* Black w/ opacity */
}

/* Modal Content/Box */
.modal-content {
    background-color: #fefefe;
    margin: 15% auto;
    /* 15% from the top and centered */
    padding: 20px;
    border: 1px solid #888;
    width: 80%;
    /* Could be more or less, depending on screen size */
}