Updated user-guide.md

Author: githubuser0xFFFF

doc/user-guide.md

@@ -493,12 +493,12 @@ auto* CentralDockArea = DockManager->setCentralWidget(CentralDockWidget);
 
 See the `centralwidget` example to learn how it works.
 
-<div style="background: #fff6e8; border: 1px solid #ffa51a; padding: 6px;"> 
-The central widget needs to be the first dock widget that is added to the
-dock manager. The function does not work and returns a nullptr if there
-are already other dock widgets registered. So setCentralWidget should be
-the first function when adding dock widgets.
-</div>
+> ##### Note
+> The central widget needs to be the first dock widget that is added to the
+> dock manager. The function does not work and returns a `nullptr` if there
+> are already other dock widgets registered. So `setCentralWidget` should be
+> the first function that you call when adding dock widgets.
+
 
 ## Styling