As technology advances and device diversity grows, web and app developers face the challenge of ensuring their projects are responsive across various screen sizes, from smartphones to large screens. CSS Media queries are essential for implementing responsive designs by using breakpoints to adjust styles according to device width. Developers can use both fixed and content-based breakpoints to achieve optimal layouts. CSS frameworks like Bootstrap and Tailwind offer predefined breakpoints, simplifying the process. Responsiveness not only enhances user experience but also impacts SEO rankings, making it crucial for developers to test their designs across multiple devices. Tools like LT Browser 2.0 provide developers with the capability to test their web pages' responsiveness on different viewports, ensuring seamless performance across all devices.