iframe {
    width:640px;
    height:480px; 
}

@media screen and (max-width:870px) {
    iframe {
        width:440px;
        height:440px; 
    }
}

@media screen and (max-width:610px) {
    iframe {
        width:380px;
        height:440px; 
    }
}

@media screen and (max-width:450px) {
    iframe {
        width:280px;
        height:440px; 
    }
}

@media screen and (max-width:340px) {
    iframe {
        width:240px;
        height:430px; 
    }
}