<!-- Style the map -->
<style>
#map {
  width: 100%;
  height: 400px;
  -webkit-filter: grayscale(100%); /* Safari 6.0 - 9.0 */
  filter: grayscale(100%);
}
</style>

<!-- Display the map -->
<div id="map"></div>

<!-- Google Maps Script -->
<script>
function myMap() {
    var mapCanvas = document.getElementById("map");
    var mapOptions = {
        center: new google.maps.LatLng(51.5, -0.2),
        zoom: 10
    };
    var map = new google.maps.Map(mapCanvas, mapOptions);
}
</script>

<script src="https://maps.googleapis.com/maps/api/js?key=YOUR_KEY&callback=myMap"></script>