Salesforce Lightning Design System (SLDS)

Salesforce released an user interface called Salesforce Lightning Design System as open source. This  provides all CSS (Cascading Style Sheets) and Images to create the Standard lightning Component instead of write CSS again for lightning Components. We can build rich enterprise experience and custom applications with the patterns using Salesforce Lightning Design System.  To build an application using SLDS we need four types of resources they are

Salesforce lightning design system

CSS framework

We can defines User Interface components using CSS framework like headers, labels, form elements, layouts, size and other visual adjustments.

Icons.

It includes PNG and SVG (both individual and spritemap) versions of our action, custom, doctype, standard and utility icons.

Font

New Salesforce Sans font is designed to give distinct visual voice bad personality to a product.

Design Tokens

These design variables allow you to tailor aspects of the visual design to match your brand. Customizable variables include colors, fonts, spacing, and sizing.

Who can use Salesforce Lightning Design System?

The new lightning design systems can be used in Visualforce pages, Lightning pages, Lightning components, Mobile Apps and other web applications. Salesforce lightning design system can be used by various Salesforce users like

Designers

The Lightning Design System reflects the patterns and components that underpin the Salesforce product. These patterns and components provide a unified language and consistent look and feel when designing apps and products within the Salesforce ecosystem.

=> Download Design System (2.4.1)

Developers

The Salesforce Lightning Design System (SLDS) component library is actively developed for Salesforce developers to create a uniform look and feel across all Salesforce  applications while adhering to CSS best practices and conventions

Lightning

Salesforce Lightning Design System is made available to Salesforce lightning components running in Salesforce lightning experience and Salesforce1 mobile application with out adding static resources for lightning components.