Alert

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

Requirements:
- Use semantic HTML (role="alert" or role="status" and aria-live="polite").
- Design: Clean, modern aesthetic with distinct variants (success, error, warning, info) using appropriate background colors, text colors, and left border accents.
- Interaction: Include an accessible close button (with aria-label="Close alert") that seamlessly dismisses the alert with a fade-out or slide-up animation.
- Icon: Provide distinct SVGs or icons for each variant (e.g. checkmark for success, exclamation mark for error).
- Accessibility: Must be fully screen reader friendly. The close button must be keyboard focusable (Tab to focus, Space/Enter to activate).
- Provide a single HTML file containing all necessary styles and scripts.