JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://maps.googleapis.com/maps/api/js?v=3.exp&libraries=geometry&sensor=false"></script>

<div id="map-canvas"></div>

<div id="overlay"><h2>I am an overlay-div</h2></div>

CSS

html, body {
  height: 100%;
  margin: 0;
  padding: 0;
}

#map-canvas{
  height: 100%;
}

#overlay {
  background-color: white;
  height: 80%;
  width: 100%;   
}

JavaScript

function initialize() {
    var mapOptions = {
    zoom: 6,
    center: new google.maps.LatLng(56.05, 10.4),
    mapTypeId: google.maps.MapTypeId.TERRAIN
  };

  var map = new google.maps.Map(document.getElementById('map-canvas'), mapOptions);
  
  //add overlay
  map.controls[google.maps.ControlPosition.RIGHT_BOTTOM].push(document.getElementById('overlay'));
}

google.maps.event.addDomListener(window, 'load', initialize);