When designing for compact or narrow interfaces, such as sidebars seen in Figma, Webflow, or Photoshop, it is important to choose a UI library that emphasizes efficient use of space and provides components optimized for density. Some libraries known for their suitability in such scenarios include:
Blueprint: Developed by Palantir, Blueprint is a React-based UI toolkit for the web that is well-suited for building complex and data-dense interfaces. It provides a range of components that can be elegantly implemented in narrow layouts without sacrificing user experience.
Material-UI (MUI): MUI is a popular React component library that follows Google’s Material Design principles. While it is versatile for various layouts, it offers customization options to suit smaller, more compact interfaces through efficient use of margins, paddings, and responsive utilities.
Ant Design: Ant Design is a design system based on a set of well-designed components that are useful for creating business applications. Its grid system and highly customizable components make it a good choice for creating dense, information-rich sidebars.
Chakra UI: Known for its simplicity and flexibility, Chakra UI provides accessible and composable components. Although not specifically designed for cramped interfaces, its flexibility allows developers to adjust styles easily to fit the needs of compact sidebars.
Fluent UI: Developed by Microsoft, Fluent UI is optimized for creating modern, responsive web experiences. Its scalable approaches to typography and spacing make it a viable option for constructing narrow interfaces.

When selecting a library, consider its adaptability to your specific design requirements, such as support for responsive and dynamic layouts, ease of customization, performance considerations, and the type of content you aim to accommodate within these compact spaces. Additionally, leveraging CSS frameworks or utility libraries like Tailwind CSS can further assist in managing the spatial dynamics required for narrow interfaces.