Add OSM liberty dark theme

public_html/index.html

@@ -228,6 +228,20 @@ Preservation of this notice shall satisfy the attribution requirement.
 
     <h4>Dark</h4>
     <div class="row">
+        <div class="col-12 col-sm-6 col-md-4 mb-4">
+            <div class="card">
+                <img src="img/osm-liberty-dark-large.png" class="card-img" alt="">
+                <div class="card-img-overlay">
+                    <div>
+                        <a class="h5 card-title" href="/styles/osm-liberty-dark/#2/0/0">
+                            OSM Liberty Dark
+                        </a>
+                        <p class="card-text">Map with 3D buildings and Natural Earth terrain shading at low zoom, dark mode.</p>
+                        <code class="card-text">https://maps.netsyms.net/styles/osm-liberty-dark/style.json</code>
+                    </div>
+                </div>
+            </div>
+        </div>
         <div class="col-12 col-sm-6 col-md-4 mb-4">
             <div class="card">
                 <img src="img/dark-matter-large.png" class="card-img" alt="">