HTML (HyperText Markup Language) is the standard markup language for documents designed to be displayed in a web browser. It can structure content from headings to links and media.
CSS (Cascading Style Sheets) describes how HTML elements should be displayed. It controls layout, colors, typography, spacing, and many visual effects to enhance web pages.
Accessible expand/collapse widgets update aria-expanded on the control and reveal or hide the content region in a way that assistive technologies can announce to users.