CSS overflow is an essential concept in web design that addresses the challenge of content exceeding the boundaries of its container, which can disrupt the layout and visibility of other elements on a page. Understanding the CSS box model is crucial, as it dictates that each element has its own box, and when content spills out of this box, it is considered overflow. The overflow property offers several values, including visible, hidden, scroll, and auto, each defining how overflowing content is handled—either by displaying it outside the box, hiding it, adding scrollbars, or only adding them when necessary. Responsiveness is a key reason to manage overflow effectively, as users access websites on various devices, and poor handling can lead to usability issues. The blog also emphasizes the importance of cross-browser compatibility and suggests using tools like LambdaTest for testing across different browsers and operating systems. Additionally, the LT Browser tool is recommended for checking website responsiveness across multiple devices and network conditions, helping developers ensure a seamless user experience.