Understanding the CSS Cascade

The cascade is a core concept in CSS—after all, it’s the “C” in Cascading Style Sheets. But what exactly does it mean?

What Is the Cascade?

The cascade is the algorithm CSS uses to determine which styles apply to each element on a web page. It resolves conflicts when multiple rules target the same property and element, and it decides which rule wins.

This decision-making process considers four key factors:

  • Specificity – How precisely a rule targets an element
  • Importance – Whether a rule is marked as !important
  • Inheritance – Whether the property is inherited from a parent element
  • Source Order – The order in which rules appear in the stylesheet

Together, these rules form a hierarchy that CSS uses to apply styles consistently.

Where Do CSS Rules Come From?

Even if your page loads just one CSS file, multiple sources of styles are involved:

  1. Browser default styles (User Agent Stylesheets) Every browser has its own built-in CSS rules for rendering HTML elements. These defaults vary across browsers.
  2. Author stylesheets (Your CSS) These are the styles you write and link to your HTML.
  3. User stylesheets Users can apply their own styles via browser settings or extensions.

All these layers interact during rendering, and the cascade ensures the correct styles are applied.

Resolving Conflicts

When two or more rules target the same property on the same element, the cascade steps in to resolve the conflict based on the factors above. This ensures predictable and consistent styling across browsers and devices.

Up next: we’ll explore specificity and inheritance in detail—two pillars of the cascade that every developer should master.