@media (max-width: 767px) {
    ._df_book {
        max-height: 350px
    }
}
@media (min-width: 768px) and (max-width: 991px) {
    ._df_book {
        max-height: 450px
    }
}
@media (min-width: 992px) {
    ._df_book {
        max-height: 600px
    }
}