Fix sidebar's color (#990)

Co-authored-by: Prince Rajpoot <44585452+princerajpoot20@users.noreply.github.com>%0ACo-authored-by: samz <samir.amzani@gmail.com>

Author: helios2003

apps/studio/src/components/Navigation.tsx

@@ -283,11 +283,11 @@ export const Navigation: React.FunctionComponent<NavigationProps> = ({
 
   if (!rawSpec || !document) {
     return (
-      <div className="flex flex-1 overflow-hidden h-full justify-center items-center text-2xl mx-auto px-6 text-center" style={{ backgroundColor: 'black' }}>
+      <div className="flex flex-1 overflow-hidden h-full justify-center items-center text-2xl mx-auto px-6 text-center bg-gray-800">
         {loading ?(
           <div className="rotating-wheel"></div>
         ) : (
-          <p style={{ color: 'white' }}>Empty or invalid document. Please fix errors/define AsyncAPI document.</p>
+          <p className='text-white'>Empty or invalid document. Please fix errors/define AsyncAPI document.</p>
         )
         }
       </div>