bookmark panel not showing scrollbar on adobe embedded

Hi Team, I am refereing below document for abobe annotation.

https://developer.adobe.com/document-services/docs/overview/pdf-embed-api/howtos_ui/#

I am using below configuration to enable or disable the icons,

viewerConfig = {
defaultViewMode:"FIT_WIDTH",
showAnnotationTools: true,
enableAnnotationAPIs: true,
showLeftHandPanel: true,
includePDFAnnotations: false,
enableFormFilling: false,
dockPageControls: false,
};

My problem is i am not able to scrollbar on bookmark panel.How do i enable is?