body, html {width: 100%; height: 100%; margin: 0; padding: 0}

.first-row {position: absolute;top: 0; left: 0; right: 0;}

.second-row {position: absolute; top: 50px; left: 0; right: 0; bottom: 0;}

.second-row iframe {display: block; width: 100%; height: 100%; border: none;}