#mainImg {
    display: flex;
    justify-content: center;
    align-items: center;
}

#mainImg > img {
    width: 350px;
    height: 350px;
}
#mainImg > button {
    display: inline-flex;
    justify-content: center;
    align-items: center;

    width: 40px;
    height: 40px;

    border-radius: 40px;
}

#mainImg > button:hover {
    background-color: black;
}