Common CSS Errors & How to Fix Them
Learn about the most frequent CSS mistakes developers make and how to fix them. Use our CSS validator below to check your own code.
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CSS Error Guides
Click any error for a detailed explanation, code examples, and step-by-step fix instructions.
Invalid CSS Property Value
Learn why CSS property values are invalid and how to fix them. Common mistakes with colors, units, and keywords.
Unknown CSS Property
How to fix unknown or misspelled CSS property names. Common typos and non-standard properties.
Missing Semicolon in CSS
Why missing semicolons break CSS rules and how to find them. The most common CSS syntax error.
Unclosed CSS Bracket
How unclosed curly braces break your entire stylesheet. Find and fix missing closing brackets.
Invalid CSS Color Value
Common CSS color mistakes: wrong hex codes, misspelled names, invalid rgb/hsl values. How to fix them.
Missing Unit on CSS Value
Why CSS values need units and when they don't. Fix missing px, rem, em, and other unit errors.
Duplicate CSS Property
Why duplicate properties in the same rule cause confusion. When it's intentional vs accidental.
Empty CSS Rule
Why empty CSS rules bloat your stylesheet. How to find and remove unused selectors.
Invalid CSS Selector
Common CSS selector mistakes: missing dots, wrong syntax, invalid pseudo-classes. How to fix them.
Missing Colon in CSS Declaration
What happens when you forget the colon between property and value in CSS.
Overuse of !important
Why !important makes CSS unmaintainable. How to fix specificity issues without it.
Using Floats for Layout
Why CSS floats should not be used for page layout. Modern alternatives with Flexbox and Grid.
z-index Without Position
Why z-index only works with positioned elements. Fix z-index not working by adding position.
Vendor Prefix Without Standard Property
Why -webkit-, -moz- prefixed properties need the standard version too.
CSS calc() Syntax Error
Common calc() mistakes: missing spaces around operators, wrong nesting, invalid expressions.
CSS Media Query Syntax Error
Common media query mistakes: wrong syntax, missing parentheses, invalid breakpoints.
CSS @font-face Syntax Error
Common @font-face mistakes: wrong src format, missing font-family, broken paths.
Inline Styles Overriding CSS
Why inline style attributes override your stylesheet and how to fix the specificity issue.