Friend uncomfortable with party’s sexy theme

DEAR HARRIETTE: I’m 19, and I was invited to a close friend’s major milestone birthday party. Initially, I agreed to go, but I’ve since learned that the theme is “sexy Hollywood.” The mood board my friend created and feels strongly about features tight, skimpy skirts and bralettes, which I’m not comfortable wearing. I prefer more low-key events and feel overwhelmed by the extravagant nature of this theme. I don’t want to upset my friend or mess up our friendship, but I also need to stay true to myself. How can I back out of the invite while still showing that I appreciate being asked? — Party Theme Dilemma