#Library {
   background-image: url('FOUNTAIN/600/Betakontext_SUPEREROICA_lichttheater_2019.jpg');
   height:800px;
   width: 600px;
}

#Library:hover {
   background-image: url('img/Betakontext_Supereroica_2019_15.jpg');
   width: [800]px;
   height: [600]px;
}