An expand/collapse widget, often called an accordion or disclosure widget, allows users to toggle the visibility of content. This helps in managing screen real estate and reducing cognitive load by hiding information until it is needed.

Semantic HTML provides meaning to the web page rather than just presentation. It improves accessibility for screen readers, helps with search engine optimization (SEO), and makes the code easier to maintain and understand for other developers.

We use the max-height property. By default, it is set to 0. When opened, JavaScript calculates the scrollHeight of the inner content and applies it as an inline style. This allows CSS transitions to animate smoothly from 0 to the specific height of the content.