Slightly improve styling on mobile devices

index.html

@@ -10,6 +10,9 @@
     <noscript>Sorry, but you'll need JavaScript enabled for any of this to work!</noscript>
     <aside>
       <h1>Chandler's Maps</h1>
+      <div class="ol-unselectable ol-control close" style="pointer-events: auto;">
+        <button onclick="document.body.classList.toggle('nav-open')">&lsaquo;</button>
+      </div>
     </aside>
     <div id="map"></div>
     <script type="module" src="./main.js"></script>