/* Make html and body fill the viewport */
html, body {
    height: 100%;
    margin: 0;
    padding: 0;
}

/* Your map container */
.map {
    width: 100%;
    height: 100%; /* now works */
}

/* Make iframe fill the container */
.map iframe {
    width: 100%;
    height: 100%;
    border: 0;
}