#dropZone,
#animals {
    display: flex;
    flex-flow: row nowrap;
    justify-content: space-between;
    margin-bottom: 20px;
}

#dropBoxFish,
#dropBoxMouse,
#dropBoxCat,
#dropBoxDog {
    display: flex;
    flex-flow: column nowrap;
    justify-content: center;
    align-items: center;
    height: 250px;
    width: 250px;
    border: 1px solid #aaaaaa;
    padding: 1rem;
}

img {
    object-fit: cover;
}