CSS Validation Issues — Reference

What each CSS Validator issue means, why it matters, and how to fix it — with links to MDN's CSS documentation.

The CSS Validator checks pasted CSS or a live stylesheet URL for syntax errors and common maintainability issues. Each issue it reports links here for a fuller explanation.

Unclosed or orphan bracesMissing or unmatched { } Missing selectorA rule block with no selector before it Multiple ID selectorsChaining several #ids in one selector Deep selector chainsLong descendant-combinator selectors Universal selectorUsing * broadly in a selector Duplicate propertySame property declared twice in one rule Invalid hex colorA #color value with the wrong digit count Invalid declarationsA rule body that isn't valid property: value pairs !important overuseSeveral !important flags in one rule Unrecognized at-ruleAn @-rule outside the common, well-supported set Empty or ruleless stylesheetNo CSS, or no rules detected