Errors

• Beware of broken box sizing
• Require properties appropriate for display
• Disallow duplicate properties
• Disallow empty rules
• Require use of known properties

Compatibility

• Disallow adjoining classes
• Disallow box-sizing
• Require compatible vendor prefixes
• Require all gradient definitions
• Disallow negative text-indent
• Require standard property with vendor prefix
• Require fallback colors
• Disallow star hack
• Disallow underscore hack
• Bullet-proof @font-face

Performance

• Don't use too many web fonts
• Disallow @import
• Disallow duplicate background images
• Disallow selectors that look like regexs
• Disallow universal selector
• Disallow unqualified attribute selectors
• Disallow units for 0 values
• Disallow overqualified elements
• Require shorthand properties

Maintainability & Duplication

• Disallow too many floats
• Don't use too many font sizes
• Disallow IDs in selectors
• Disallow !important

Accessibility

• Disallow outline:none

OOCSS

• Disallow qualified headings
• Heading should only be defined once

Learn More About the Rules