The CSS cascade resolves conflicts by comparing importance (!important), origin (user vs author), specificity, and source order. More specific selectors win; if specificity ties, later rules take precedence. Edge cases like !important and inline styles can override expectations; test computed styles.
How does the CSS cascade determine which styles are applied?
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Overview
The cascade is the algorithm browsers use to combine styles from different sources. When multiple rules target the same element, CSS evaluates them using a four-step hierarchy: importance, origin, specificity, and order of appearance.
Step | Concept | Explanation |
|---|---|---|
1 | Importance | Rules marked with |
2 | Origin | Inline styles > author stylesheets > user stylesheets > browser defaults. |
3 | Specificity | More specific selectors take precedence (e.g., IDs > classes > elements). |
4 | Source Order | When all else is equal, the rule defined last in the CSS wins. |
CSS
p { color: blue; } /* element selector */
.text { color: green; } /* class selector */
#intro { color: red; } /* ID selector */
p { color: purple !important; } /* overrides all */
Result: The !important rule wins even though the ID selector is more specific. Without !important, the ID selector would take priority.
Best Practices
- Keep selectors consistent and avoid unnecessary complexity.
- Minimize use of
!important; rely on proper structure and specificity instead. - Understand how frameworks (e.g., Bootstrap) use cascade layers and resets.
- Use the browser’s ‘Computed Styles’ panel to debug cascading conflicts.
The cascade is like a courtroom: importance is the judge, specificity is the lawyer’s strength, and source order is who speaks last.
Practical scenario
A component library sets button styles, and your app needs overrides. The cascade order determines whether your app styles actually win.
Common pitfalls
- Assuming later rules always win without checking specificity.
- Overusing
!importantand making future overrides impossible. - Forgetting inline styles beat most stylesheet rules.
Lower specificity is easier to maintain but may lose to library styles. Use DevTools to inspect the winning rule in the computed panel.
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