#modal {
    display: none;
    position: fixed;
    z-index: 1;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    overflow: auto;
    background-color: rgba(0,0,0,0.7);
}

#modal_content {
    width: 500px;
    background: #fff;
    margin: 15% auto;
    padding: 10px;
    position: relative;
    animation: animatetop 0.4s
}

@keyframes animatetop {
    from {
        top: -300px;
        opacity: 0
    }

    to {
        top: 0;
        opacity: 1
    }
}