The Replit design system (RUI) was created to address internal design growth pains by implementing a universal React component, providing an intuitive and easy-to-use API for designers and engineers. The team considered various libraries and approaches, including Styled JSX, styled-components, Tailwind, Style props, CSS prop (Emotion), and String literals vs Objects, before landing on a system using Emotion with object-like styles, a basic `<View>` primitive, and tailwind-like utility traits that can be mixed in. The RUI API provides a basic `<View>` component, a `css` prop powered by Emotion, and Replit CSS utilities, making it easier for designers to collaborate with engineers and improving the overall development experience.