I want you to act as a senior front-end developer specializing in pure HTML, CSS, and JS. Generate a Tabs component with multiple tabs, supporting light/dark themes, dynamic tab switching, and single source of truth for styles.

Requirements:

Semantic HTML structure for tabs and tab panels.

CSS variables for active/inactive tabs, text, background, and theming.

JS to handle tab switching, dynamic content updates, and theme toggling.

Include JSDoc comments for functions and event handlers.

Unit-testable methods for tab selection and theme switching.

Accessibility: proper ARIA roles, keyboard navigation, and focus management.

Organized files: separate HTML, CSS, JS, referencing central theme variables.