.gallery{
    border: 5px solid green;


}
li {
    display: none;
    position: absolute;
    background: cornflowerblue;
    min-width: 160px;
    box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
    padding: 12px 16px;
    z-index: 1;
}

li:hover {
    display: block; 
}