body { margin: 0; padding: 0; }
#map { position: absolute; top: 0; bottom: 0; width: 100%; }
h1 {
    position: absolute;
    top: 10px;
    left: 10px;
    z-index: 1;
    background: white;
    padding: 10px;
    border-radius: 5px;
    font-family: sans-serif;
    font-size: 1.5em;
}