HTML5 is the latest version of HTML that focuses on web applications and includes new elements such as <video>, <audio>, and <canvas>. It also provides better support for multimedia playback and offline storage. Some key features of HTML5 include new semantic elements, form controls, and drawing capabilities. While not fully standardized, all major browsers support many HTML5 features in their latest versions. CSS3 builds on CSS2 and introduces new modules for borders, backgrounds, text effects and more to create more advanced visual styles without relying on images.