Accordion

Act as a senior frontend engineer and UI specialist. Build a highly accessible, animated Accordion component in HTML, CSS, and minimal vanilla JavaScript.

Requirements:
- Use semantic HTML (details/summary or button/div with proper aria-expanded and aria-controls attributes).
- Design: Clean, minimalist borders with a subtle background color change on hover.
- Interaction: Smooth height transition when opening/closing (use CSS grid or max-height tricks).
- Icon: A chevron on the right side that rotates 180 degrees when expanded.
- Accessibility: Must be fully keyboard navigable (Tab to focus, Space/Enter to toggle) and screen reader friendly.
- Provide a single HTML file containing all necessary styles and scripts.