Login theme bugfix.

client/public/login.html

@@ -19,7 +19,9 @@
         <div id="root"></div>
         <script>
             (function() {
-                document.body.dataset.theme = 'auto';
+                var prefersDark = window.matchMedia && window.matchMedia('(prefers-color-scheme: dark)').matches;
+                var currentTheme = prefersDark ? 'dark' : 'light';
+                document.body.dataset.theme = currentTheme;
             })();
         </script>
     </body>