Hi, here is my suggestion:
myScrollBox.ClientEvents.ExtEvents.Values['afterrender']:='function afterrender(sender, eOpts) {sender.getEl().dom.style["overflow-x"]="hidden";;}';
Or
MyScrollBox -> ClientEvets -> ExtEvents -> function afterrender:
function afterrender(sender, eOpts)
{
sender.getEl().setStyle('overflow-x', 'hidden')
}