Web development has shifted from static pages to highly interactive platforms that must work smoothly on a wide range of devices. Traditional methods using only HTML, CSS, and JavaScript often fail to deliver the speed, responsiveness, and flexibility expected by modern users. This research explores how combining React, responsive design techniques, and Progressive Web App (PWA) features can solve these limitations and create scalable, efficient, and user-friendly applications. The study focuses on the development of a prototype e-learning platform that demonstrates these technologies in practice. React is used for building reusable components and reducing code repetition, while responsive design ensures that the layout adapts across multiple screen sizes without compromising usability. PWA features add offline access, push notifications, and installability, giving the web app an app-like experience without requiring separate native development. The system is tested for performance, responsiveness, and user interaction across different devices. Results show that this combined approach provides faster load times, simpler maintenance, and a more engaging user experience compared to traditional web design. The work highlights how modern web technologies can be effectively integrated to address common challenges in cross-platform web development, while also offering a practical solution for scalable educational platforms.