Tailored for building Salesforce apps: Using the Lightning Design System markup and CSS framework results in UIs that reflect the Salesforce Lightning look and feel.
Continuously updated: As long as you’re using the latest version of the Lightning Design System, your pages are always up to date with Salesforce UI changes.
icons/ - PNG, SVG and SVG spritemap versions of icons
images/ - including spinners
styles/
salesforce-lightning-design-system.css (regular CSS — which should not be used within a component that already has access to the SLDS CSS within the platform — please use the scoping tool mentioned below)