css-responsive-google-map-iframe From https://blog.kulturbanause.de/2012/10/google-maps-im-responsive-webdesign/
.responsiveContainer {
position: relative;
padding-bottom: 56%;
height: 0;
overflow: hidden;
}
.responsiveContainer iframe {
position: absolute;
top: 0;
left: 0;
width: 100%;
height: 100%;
}
<div class="responsiveContainer">
<!-- iframe-Code von Google Maps -->
</div>