A CSS framework is a library allowing for easier, more standards-compliant web design using the Cascading Style Sheets language. Most of these frameworks contain at least a grid. More functional frameworks also come with more features and additional JavaScript based functions, but are mostly design oriented and focused around interactive UI patterns. This detail differentiates CSS frameworks from other JavaScript frameworks.

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Two notable and widely used examples are Bootstrap and Foundation.

CSS frameworks offer different modules and tools:

• reset style sheet
• grid especially for responsive web design
• web typography
• set of icons in sprites or icon fonts
• styling for tooltips, buttons, elements of forms
• parts of graphical user interfaces like accordion, tabs, slideshow or modal windows (Lightbox)
• equalizer to create equal height content
• often used CSS helper classes (left, hide)

Bigger frameworks use a CSS interpreter like Less or Sass.

• Comparison of layout engines (Cascading Style Sheets)