feat(ui): changed Background color, centered Lobby

Added a background color for the mainmenu and the lobby + centered lobby

knockoutwhistweb/app/assets/stylesheets/dark-mode.less

@@ -3,7 +3,7 @@
     --background-image: url('/assets/images/background.png') !important;
     --color: #f8f9fa !important; /* Light text on dark bg */
     --highlightscolor: rgba(131, 131, 131, 0.75) !important;
-
+    --background-color: #192734;
     /* Bootstrap variable overrides for dark mode */
     --bs-body-color: var(--color);
     --bs-link-color: #66b2ff;

knockoutwhistweb/app/assets/stylesheets/light-mode.less

@@ -2,4 +2,5 @@
   --background-image: url('/assets/images/img.png');
   --color: black;
   --highlightscolor: rgba(0, 0, 0, 0.75);
+  --background-color: rgba(228, 232, 237, 1);
 }

knockoutwhistweb/app/assets/stylesheets/main.less

@@ -14,7 +14,7 @@
   --bs-border-color: rgba(0, 0, 0, 0.125) !important;
   --bs-heading-color: var(--color) !important;
 }
-
+@background-color: var(--background-color);
 @highlightcolor: var(--highlightscolor);
 @background-image: var(--background-image);
 @color: var(--color);
@@ -29,6 +29,10 @@
     background-repeat: no-repeat;
     background-attachment: fixed;
 }
+.lobby-background {
+    background-color: @background-color;
+
+}
 
 .navbar-header{
     text-align:center;