Cascade
The CSS cascade is the set of rules used to resolve which declarations apply when multiple declarations target the same property on the same element.
The cascade considers origin, importance, cascade layers, specificity and source order. Understanding it reduces unnecessary overrides and excessive use of !important.
How CSS decides the final value
The cascade considers origin, importance, cascade layers, specificity and source order. Understanding it reduces unnecessary overrides and excessive use of !important. In practical terms, Cascade belongs to the presentation and layout layer. Knowing that layer is important because it tells you what the term can change, what it cannot change, and where to look when something behaves unexpectedly.
Tracing competing declarations to one result
Two rules may target the same property; origin, importance, cascade layer, specificity and source order determine the winner.
Where origin, layer and specificity meet
You do not need to memorize the term in isolation. It becomes useful when you can recognize it in the tool, browser, file or conversation where the concept is doing real work.
The cascade is bigger than specificity
The CSS cascade is the set of rules used to resolve which declarations apply when multiple declarations target the same property on the same element. By contrast, Specificity is the weighting system CSS uses when competing selectors from the same cascade origin and layer match the same element. The two can appear in the same project, but they describe different parts of the work and should not be used as interchangeable labels.
The mistake: debugging one selector in isolation
The common mistake is to use Cascade as if it also meant Specificity. That blurs two separate decisions and usually sends troubleshooting in the wrong direction. A better test is practical: Trace the winning declaration in computed styles rather than reading the stylesheet from top to bottom and guessing.
Why the final value has a traceable history
In day-to-day work, Cascade matters when the concept needs to be identified precisely instead of being grouped with a nearby term. The practical value is not the vocabulary itself; it is being able to identify the right control, file, setting or decision when the concept becomes relevant.
Two rules may target the same property; origin, importance, cascade layer, specificity and source order determine the winner. That example is useful because it turns the definition into something you can recognize, test and discuss with other people working on the same project.
Related terms worth learning next
Sources and further reading
Use these references when you need documentation-level detail, specifications or product-specific behavior beyond the plain-English explanation above.