parent should have display flex

Viewer/dist/ufoExample.html

@@ -10,9 +10,7 @@
             babylon,
             #viewport {
                 /*max-width: 900px;
-                max-height: 600px;
-                width: 100%;
-                height: 600px;*/
+                max-height: 600px;*/
             }
         </style>
     </head>

Viewer/src/viewer/defaultViewer.ts

@@ -221,6 +221,7 @@ export class DefaultViewer extends AbstractViewer {
     protected _prepareContainerElement() {
         this.containerElement.style.position = 'relative';
         this.containerElement.style.height = '100%';
+        this.containerElement.style.display = 'flex';
     }
 
     /**