Flexible web design should be fully proportional for multiple devices. Flexible or responsive websites are those that automatically adjust to fit multiple screen sizes. For the designer and developer, it means that they only have to work on one version of a website instead of designing one for computers and another for mobile devices.
A few years ago, creating a fixed website was practical. Fixed-width layouts are easier to create than flexible ones - the layouts don't break and content doesn't overflow. However, after smartphones, netbooks and tablets burst onto the scene, creating websites to fit smaller screens became absolutely crucial. Previously, mobile versions of websites were a suitable solution for many devices, but due to the vast quantity of different screen sizes available today, flexible design is the best solution right now. CSS Grid and Flexbox are modern CSS layout technologies that provide powerful and efficient ways to create grid-based and flexible layouts for websites and applications.