What principle focuses on ensuring a solution works across various browsers and devices?

The principle that focuses on ensuring a solution works across various browsers and devices is flexibility. Flexibility in design refers to the ability of a solution to adapt and perform well under different conditions and contexts. This includes automatically adjusting to various screen sizes, operating systems, and web browsers, ensuring that users have a consistent and functional experience no matter how they access the solution.

A flexible design approach often involves responsive design techniques, which allow web pages to reflow and resize elements appropriately. This adaptability is crucial as users access content on an increasingly varied array of devices, including smartphones, tablets, and desktops. By prioritizing flexibility, developers and designers can create robust applications that meet the needs of a diverse user base, providing seamless functionality regardless of device or browser choice.