html, body, #map {
  margin: 0;
  padding: 0;
  width: 100%;
  height: 100%;
  overflow: hidden;
}

#map {
  position: relative;
}

#controls, #parties, #axes, #heatmap {
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
}

#controls { z-index: 150; }
#parties  { z-index: 100; }
#axes     { z-index: 50;  }
#heatmap  { z-index: 1;   }

/* Vertical axis */
#axes:before {
  content: '';
  position: absolute;
  left: 50%;
  top: 0;
  width: 1px;
  height: 100%;
  background-color: darkgrey;
}

/* Horizontal axis */
#axes:after {
  content: '';
  position: absolute;
  top: 50%;
  left: 0;
  height: 1px;
  width: 100%;
  background-color: darkgrey;
}

.party {
  position: absolute;
  width: 200px;
  margin-top: -0.6em;
  margin-left: -100px;
  text-align: center;
  color: white;
  font: 2em Tahoma;
  text-shadow: 0px 0px 10px rgba(0,0,0,0.4);
}

#controls {
  text-align: right;
  padding: 1em;
  pointer-events: none;
}
#controls select, #controls button {
  font: 1.2em Tahoma;
  pointer-events: auto;
}