Bună ziua! The meaning of 단정하다 and 깔끔하다 are quite similar. There are some differences in nuance. 단정하다 has the nuance of propriety.(be in good order) 단정하다 is used for appearance or attitude of a person.(올바른 상태) 깔끔하다 has the nuance of cleanness.(not dirty.)(깨끗한 상태) 깔끔하다 is used not only for appearance, attitude, character of a person but also for the clean situation. 그녀는 옷차림이 깔끔하다(O) 그녀는 옷차림이 단정하다(O) 아나운서의 깔끔한 진행이 이번 대회를 더욱 돋보이게 했다.(O) 아나운서의 단정한 진행이 이번 대회를 더욱 돋보이게 했다.(X) 도로를 깔끔하게 정비하다 (O) 도로를 단정하게 정비하다 (X)

단정하다is just used to the clothing or body shape but 깔끔하다has larger concept than 단정하다. We can use 깔끔하다 to our clothing or body part but also use to place (like neat room), stylish design. its often used to express sth very arranged.

단정하다 is more etiquette related while it's more of "minimalism", "clearness" with 깔끔하다. 단정하다 suits "dress code" while 깔끔하다 belongs to "style" 단정하다 tends to be of "complementary colors" (soft tone) while 깔끔하다 being of "primary colors" (high contrast) e.g 교복을 단정하게 차려입은 학생: a student wearing the school uniform in compliance with the dress code. 청바지에 흰 셔츠만으로 깔끔한 멋 발산: emitting simplistic charm by wearing blue jeans plus white shirt.