Cesium tab sequence ion icon causes white region on right side of browser


I have a strange behaviour in the tab sequence at the browser.

Sitting on the Cesium ion icon using the tab will shift the viewer window and on the right a white part is appearing.



This happens in chrome as well in edge.

Has anyone a similar behaviour ? Where can I fix it.

In my application there are no other widgets switched on. I see that sometimes the tab in this stage will go to a search field and on other sandcastle demos it will go to the browser menu.

Can this influence the behaviour ?