diff --git a/static/index.html b/static/index.html
index 70b64ed..0065d62 100644
--- a/static/index.html
+++ b/static/index.html
@@ -14,6 +14,9 @@
       width: 100%;
       background-color: black;
     }
+    .grayscale {
+      filter: saturate(0.4);
+    }
   </style>
   <!-- TODO: self-host -->
   <link rel="stylesheet" href="https://mfhsieh.github.io/leaflet-simple-locate/examples/demo.css" />