The CSS Cascade determines which CSS rule applies when multiple rules target the same HTML element. It helps the browser decide which styles to use when different declarations conflict.
Understanding the CSS Cascade is important when learning CSS Selectors and CSS Specificity.
How Does the CSS Cascade Work?
When multiple CSS rules apply to the same element, the browser considers several factors, including:
- Importance: Declarations marked with
!importantcan override normal declarations. - Cascade origin and layers: The source of a declaration and its cascade layer affect its priority.
- Specificity: More specific selectors generally take priority over less specific selectors.
- Source order: If competing declarations have equal priority and specificity, the later declaration usually wins.
The browser evaluates these factors to determine the final style of an element.
CSS Cascade Example
Consider the following HTML and CSS:
<!DOCTYPE html>
<html>
<head>
<style>
p {
color: blue;
}
p {
color: red;
}
</style>
</head>
<body>
<p>This is a CSS Cascade example.</p>
</body>
</html>Output: The paragraph appears red.
Both CSS rules target the same paragraph and have equal specificity. Because the red declaration appears later, it takes precedence.
CSS Cascade with Specificity
Consider another example:
<style>
p {
color: blue;
}
.highlight {
color: green;
}
</style>
<p class="highlight">Learn CSS with Web4Learners.</p>The paragraph appears green because the class selector .highlight has greater specificity than the element selector p.
You can learn more in our CSS Specificity tutorial.
Why Is the CSS Cascade Important?
The CSS Cascade helps developers understand why a particular style appears on a webpage. It is especially useful when debugging conflicting styles or working with multiple stylesheets.
When you understand how the cascade works, you can write clearer CSS and troubleshoot styling problems more easily.