Progressive Enhancement is a web design strategy focused on creating cross-browser compatible websites by prioritizing core content and functionality while progressively adding advanced features. This approach ensures that essential elements of a webpage remain accessible to users irrespective of the browser version they use, addressing the challenge posed by varying browser standards. Unlike Graceful Degradation, which designs for the latest browsers first and then scales down, Progressive Enhancement starts with a minimal viable product and builds up, making it more effective for SEO and user accessibility. The methodology involves three layers: the Content Layer with semantic HTML for structure, the Presentation Layer using CSS for styling, and the Scripting Behaviors Layer with JavaScript for functionality. Cross-browser testing, such as that offered by LambdaTest, is crucial for ensuring website compatibility across different browsers, with tools available for real-time, automated, and responsive testing.