Add --microsoft-blue-darker as css variable

src/devpanel/index.css

@@ -5,6 +5,7 @@
   --microsoft-gray-lighter: #d2d2d2;
   --microsoft-gray-lightest: #e6e6e6;
   --microsoft-white: #fff;
+  --microsoft-blue-darker: #005499;
   --microsoft-blue: #0078d7;
   --microsoft-blue-lighter: #99d1ff;
   --microsoft-orange: #d83b01;