Salesforce Lightning Design System is…
Flexible
Start building immediately, without worrying about detailed specs. SLDS lets you focus on the big picture to deliver the best possible user experience.
Scalable
Manage design at scale, with a living design system that evolves as needs change. SLDS keeps apps, interfaces, and tools consistent no matter how fast the system grows.
Efficient
SLDS saves time and energy, freeing designers and developers to focus on larger issues of usability and meaning. Standardized, reusable components support collaboration, reinforce branding, and provide a consistent look and user experience.
Accessible
Salesforce is committed to creating products that are perceivable, operable, understandable, and robust for all users. All SLDS components include ARIA markup and guidelines to help people with disabilities use and contribute to Salesforce applications.
Living
SLDS is a living open-source design system. Our UX team rolls out new UI updates with every release, expanding the design possibilities while keeping existing applications up to date and running seamlessly.
Platform Agnostic
Use the SLDS CSS framework with any tech stack you can dream up, or take advantage of our guidance on using SLDS with Salesforce technologies including Lightning Web Components, Aura, and Visualforce.
Lightning Design System
https://www.lightningdesignsystem.com/