To fix issue #5009, add width attribute to .sidebar (#5107)

Author: mohammadbaghaei

packages/modelviewer.dev/styles/examples.css

@@ -64,6 +64,7 @@ select {
 }
 
 .sidebar {
+  width: var(--sidebar-width);
   margin: 0;
   padding: 0;
   background-color: #f6f6f6;