style.css

/* 
 * Always set the map height explicitly to define the size of the div element
 * that contains the map. 
 */
 #map {
    height: 100%;
  }
  
  /* 
   * Optional: Makes the sample page fill the window. 
   */
  html,
  body {
    height: 100%;
    margin: 0;
    padding: 0;
  }
  
  #container,
  #left,
  #right,
  .map,
  .gutter {
    height: 930px;
  }
  
  #left,
  #right,
  .gutter {
    float: left;
    position: relative;
    overflow: hidden;
  }
  
  #map-left {
    position: absolute;
    left: 0;
    top: 0;
  }
  
  #map-right {
    position: absolute;
    right: 0;
    top: 0;
  }
  
  .gutter {
    background-color: #133467dd;
    background-repeat: no-repeat;
    background-position: 50%;
  }
  
  .gutter.gutter-horizontal {
    cursor: col-resize;
    background-image: url("data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAeCAYAAADkftS9AAAAIklEQVQoU2M4c+bMfxAGAgYYmwGrIIiDjrELjpo5aiZeMwF+yNnOs5KSvgAAAABJRU5ErkJggg==");
  }