Developer.WordPress.org

WordPress Theme Developer Handbook serves as a comprehensive guide for building WordPress themes, covering both modern block themes (available from WordPress 5.9) and classic themes. Block themes use HTML and configuration files with full Site Editor compatibility, while classic themes rely on PHP, JavaScript, and CSS with WordPress functions and hooks. The handbook provides structured learning from basic concepts to advanced topics, including development environment setup, core concepts, child themes, testing practices, and theme distribution guidelines for the WordPress.org directory.