I am Lokeshwar i was working on migration of SharePoint from 2010 to 2016.
We have some Nintex forms which is migrated from SP2010 to SP2016.
Observation in 2016 : If there is required field validation for dropdown then without filling anything when you click on save then it shows hover highlight in red color on parent div of dropdown control instead of select.
Whereas in SharePoint 2010 we have hover highlight in red color for dropdown control for required field validation.
Added attachments for reference .
Please help me out to understand if this is default behavior in SP2016 or do we have any fix to make it hover for select instead of parent div of dropdown control in SP2016.