/* Kann maximal 768px darstellen. */ 
@media only screen and (max-width : 768px) { 
/* CSS hier */

.iframe_talks {
 width: auto;
 height: auto;
}

}

@media only screen and (min-width: 1280px) {

.iframe_talks {
 width: 560px;
 height: 315px;
}

}