Note, including skirt’s leitmotif (5)
I believe the answer is:
'leitmotif' is the definition.
(I've seen this before)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for theme that I've seen before include "Recurrent unifying idea" , "Thread, melody" , "He met (anag) - subject" , "A subject or repeated melody" , "idea of the work" .)