Foreign key in main table or supplementary table? I have two tables with one to one relationship b/w student and Student_detail(kind of supplementary table) table

Design 1

Student
 student_id
 name
 ....


Student_detail

 student_detail_id
  student_id(foreign key to student_id in student table)
  ...


Design 2

Student
 student_id
 name
 student_detail_id (foreign key to student_detail_id in Student_detail table)
 ....


Student_detail

 student_detail_id
   ...


My question is which approach is better ? From design perspective is it better to keep the foreign key in main table(in this case student table) or
in supplementary table (student_detail table ) ?

Per my understanding approach 2 is better as if we add more supplementary tables we don't have to modify main table ?
Suggested that previous comment be posted as 'answer'.  Here 'tis.

Even if a justifiable one-to-one, I'd still treat the "primary" table as if it were a parent, and the "detail" as if it were one of  potentially multiple children. Thus the FK would go in the 'details' table. More appropriately named 'additional_student_details'.