Add css in 404,422,500 pages

Added some styling in 404,422,500

public/404.html

@@ -16,8 +16,8 @@
           <h1 class="title is-size-1">404</h1>
           <h1 class="title is-size-5">The page you were looking for doesn't exist.</h1>
           <p>You may have mistyped the address or the page may have moved.</p>
-
-          <p>If you are the application owner check the logs for more information.</p>
+          <p>If you are the application owner check the logs for more information.</p><br><br>
+          <button class="button">Back to previous page</button>
         </div>
       </div>
     </div>