The clickable header of a PhoenixPaper.Accordion (pp_accordion_summary/1)
— a <label> pointing at the accordion's hidden checkbox/radio, with a
trailing expand icon that rotates via peer-checked:. See
PhoenixPaper.Accordion's moduledoc for a full example.
id must be the same id passed to the parent pp_accordion/1 — it's
how this label finds the right checkbox to point for= at.
Summary
Functions
Renders an accordion summary/header. See the module doc.