body { margin: 0; padding: 0; }

#map { position: absolute; top: 0; bottom: 0; width: 100%; }

.btn-control {
  font:
    bold 12px/20px 'Helvetica Neue',
    Arial,
    Helvetica,
    sans-serif;
  background-color: #3386c0;
  color: #fff;
  position: absolute;
  top: 20px;
  left: 50%;
  z-index: 1;
  border: none;
  width: 200px;
  margin-left: -100px;
  display: block;
  cursor: pointer;
  padding: 10px 20px;
  border-radius: 3px;
}

.btn-control:hover {
    background-color: #4ea0da;
}