The CSS diff tool compares two CSS files at two levels: selector-level diff groups changes by rule block so you can see which selectors were added, removed, or had their properties changed; line-level diff gives you the raw text comparison with CSS syntax highlighting. Use both views together to understand the full scope of stylesheet changes.
How to Use the CSS Diff Tool
Comparing CSS stylesheets is a regular task when reviewing pull requests, auditing theme changes, or debugging why a component looks different between environments. Our free CSS diff tool offers two complementary views: a selector-level diff that groups changes by CSS rule, and a line-level diff for raw text comparison with syntax highlighting.
Step 1: Paste Your CSS Files
Paste the original (older) CSS into the left panel and the modified (newer) version into the right panel. The tool works with any standard CSS: component stylesheets, full site stylesheets, CSS resets, utility classes, or CSS custom property declarations. For best results in selector-level mode, use formatted (not minified) CSS.
Step 2: Click Compare CSS
Click Compare CSS to run both diff algorithms simultaneously. The selector-level parser extracts all CSS rules using { } block detection, maps each selector to its properties, then compares selectors and properties between the two files. The line-level diff uses LCS comparison on the raw text lines.
Step 3: Read the Selector-Level View
In selector-level view, each CSS rule block is shown as a card. Green cards are new selectors only in the modified file. Red cards are removed selectors only in the original. Yellow cards are selectors that exist in both files but have changed properties. For changed selectors, individual property rows show which values changed — original value on the left, new value on the right.
Step 4: Use Line-Level View for Details
Switch to "Line Level" view for a side-by-side text comparison with CSS syntax highlighting: selectors in blue, property names in pink, values in orange, and at-rules in purple. This is useful when you need to see the exact whitespace, comments, or vendor-prefixed properties that changed.
Stats Summary
The stats bar shows selectors added, removed, properties changed (within matching selectors), and selectors unchanged. This gives you a quick summary of the scope of CSS changes before reading the detailed diff output.
FAQ
Is this CSS diff tool free?
Yes, completely free with no account or signup required. All CSS comparison runs in your browser — your stylesheet code is never sent to any server.
Is my CSS code private?
Yes. The entire diff computation runs in client-side JavaScript. Nothing is uploaded or stored. You can safely use this tool with proprietary stylesheets, internal design system code, or unreleased CSS frameworks.
What is selector-level diff versus line-level diff?
Selector-level diff parses both CSS files into rule blocks (selector + properties), then compares at the rule level — showing which selectors were added, removed, or had their properties changed. Line-level diff is a standard text comparison showing exactly which lines changed. Selector-level is better for understanding structural changes; line-level is better for reviewing exact values.
Can I compare SCSS or Less files?
The tool works best with compiled, standard CSS. SCSS/Less with nesting, variables, and mixins will be treated as plain text in selector-level mode, which may not parse correctly. Use the line-level diff view for SCSS/Less comparison — it will show all text changes accurately.
What does CSS specificity have to do with diff?
This tool focuses on structural and value differences, not specificity analysis. If you need to understand which selector wins in a specificity conflict, use our CSS Specificity Calculator tool. The diff tool tells you what changed; specificity analysis tells you which rule applies.
Can I compare minified CSS?
Yes, the CSS parser handles minified CSS by splitting on { and } delimiters. For better readability in line-level diff view, consider formatting the CSS first with a CSS formatter tool, then comparing.