Mandatory Fields in WD4A

hi all,,

I have added 1 custom field in ESS standard create travel request form. it is in WD4A and i have to make that field mandatory . i have specified the state property of this UI as 'Required', The UI is DropDownByKey. but still it is allowing to navigate in the next view even if i have not selected any value and in this fields (i.e the fields is blank). How to stop this navigation????.

also other standard mandatory fields of this view come up with red Color (*) before field but my custom fields is not.. So is there any way to achieve this??