Create and Define Fields of Data Types

When I want to create new data type or option set, I can only create new but I can not add fields for characteristics of the data type.
There is no option on the screen “add new characteristics”… the buttons are simply disappeared.
Please some advice, cause everything worked good until yesterday.

Could you show an example?

Normally fields are actually called attributes in option sets.

And you can not click on data type name or option set name