Which design approach provides custom layouts based on the browser window size?

Responsive Web Design is the approach that provides custom layouts based on the browser window size. This method uses fluid grids, flexible images, and media queries to adjust the layout and design of a website dynamically according to the dimensions of the user's screen. As the browser window is resized, the design elements rearrange and resize to create an optimal viewing experience across a variety of devices, from desktop monitors to tablets and smartphones. This fluidity ensures that users have a consistent and user-friendly experience regardless of the device they are using.

On the other hand, while Adaptive Design also adjusts layouts, it typically relies on predefined specific layouts for certain device sizes rather than fluidly adapting across a range of sizes. Mobile Friendly Design focuses more on creating a version of the site that is usable on mobile devices, but it may not provide the same level of customization based on varying screen sizes. Static Web Design, however, does not adapt at all; it presents the same layout regardless of the browser window size, making it less effective for contemporary web design needs.