CSS Diff & Compare
Compare two CSS stylesheets and identify meaningful source-structure differences without confusing formatting noise with real changes.
How to compare CSS
- Paste the original in CSS Document A.
- Paste the modified in CSS Document B.
- Click Compare CSS.
What this CSS diff compares
- Rules, declarations, values.
- Custom properties.
- Nested rules.
- At-rules and source/cascade-sensitive order.
What formatting differences are ignored
- Indentation and line breaks.
- Whitespace around structural punctuation.
- Combinator spacing in selectors.
Why declaration order matters in CSS
- Duplicate declarations.
- Fallbacks.
- Shorthand vs. longhand.
- Custom properties.
When CSS diff is useful
Comparing two stylesheets is useful whenever CSS changes over time and you need to know exactly what was edited: reviewing a revision to a shared stylesheet before merging it, checking what a theme update actually changed across selectors and custom properties, or narrowing down which rule introduced a visual regression by comparing the working version against the one that broke.
Selectors, declarations, and values
The diff reports on changes at each level of a rule: a selector added, removed, or rewritten; a declaration added or dropped from a rule body; and a property's value changed, even if the property itself stays the same. Because a single-character change to a value, like a color or a spacing unit, can have a real visual effect, value changes are surfaced just as prominently as structural ones.
Formatting differences vs. meaningful changes
Indentation, line breaks, and spacing around braces or colons don't change how a browser interprets a stylesheet, so this diff normalizes that whitespace and focuses on differences that actually affect the cascade. That keeps a reformatted file from swamping the results with noise when nothing about the actual styling changed.
Reviewing CSS changes safely
Pay close attention to declaration order within a rule when duplicate properties are involved, since the diff can show a value moved rather than removed if the cascade outcome depends on which one comes last. When comparing a theme or component update, checking custom property changes first often explains a cluster of other visual differences at once, since many values elsewhere may reference the same variable.
Frequently asked questions
- Does this CSS diff upload my code?
- No. Both stylesheets are parsed and compared in your browser.
- Does indentation affect the result?
- No. Whitespace between tokens is normalized.
- Does declaration order matter?
- Yes. Declaration order can affect the cascade.
- Are duplicate declarations compared separately?
- Yes. If a property appears more than once in a rule, each occurrence is tracked individually, since the later one is what actually wins in the cascade.
- Is this a good way to review a theme or design-system update?
- Yes. Pasting the before and after CSS for a theme, component library, or design-token file makes it easy to see exactly which selectors, values, or custom properties changed, which is often faster than scanning a large stylesheet by eye for what moved.