<!DOCTYPE html>
<html>
  <head>
    <style>
      #map {
        width: 55%;
        padding: 20% 20% 20% 20%;
      }
    </style>
  </head>
  <body>
    <h1>
      Find today's local shows, concerts, and events in your area!
    </h1>
    Enter your zip code: <input type="text" name="zipcode"><br>
    <input type="submit" value="Submit">
    <div id="map"></div>
    <script src="https://maps.googleapis.com/maps/api/js?callback=initMap" async defer></script>
    <script>
      function initMap() {
        var mapDiv = document.getElementById('map');
        var map = new google.maps.Map(mapDiv, {
          center: {lat: 44.540, lng: -78.546},
          zoom: 7
        });
      }
    </script>
  </body>
</html>

<!DOCTYPE html>
<html>
  <head>
    <style>
      #map {
        width: 55%;
        padding: 20% 20% 20% 20%;
      }
    </style>
  </head>
  <body>
    <h1>
      Find today's local shows, concerts, and events in your area!
    </h1>
    <h2>
      Enter your zip code: <input type="text" name="zipcode"><br>
      <input type="submit" value="Submit">
    </h2>
    <div id="map"></div>
    <script src="https://maps.googleapis.com/maps/api/js?callback=initMap" async defer></script>
    <script>
      function initMap() {
        var mapDiv = document.getElementById('map');
        var map = new google.maps.Map(mapDiv, {
          center: {lat: 44.540, lng: -78.546},
          zoom: 7
        });
      }
    </script>
  </body>
</html>

Move input field to <h2> HTML tag
Move input field to <h2> HTML tag
