In CSS, "cascade" refers to the browser's algorithm to resolve style conflicts. It determines which rule takes effect through selector specificity, source order and style source. For example, when two rules conflict, selectors with higher specificity take precedence; if the specificity is the same, the subsequent rules win; in addition, the priority of user agent, user and author styles also work. !important can be forced to cover, but should be used with caution. Managing the CSS structure, naming specifications and debugging tools can effectively improve the control of cascade.
When you're working with CSS, "cascade" is one of those terms that come up often — and for good reason. It's what determines which styles actually get applied to your HTML elements when there are conflicting rules.
So, what is the cascade in CSS? Simply put, it's the algorithm browsers use to decide which CSS rule wins when multiple rules could apply to the same element. It's not just about which selector matches — it's also about specification, source order, and where the styles come from.
Here's how it really works.
How Browsers Choose Between Conflicting Styles
Imagine you have two CSS rules that both target the same <p></p> element:
p {
color: blue;
}
.special {
color: red;
}And your HTML looks like this:
<p class="special">Hello</p>
Which color do you think wins?
The answer is red — because .special has higher specificity than a plain element selector. That's the cascade in action.
But it's not always that straightforward. The browser considers several factors:
- Selector specification
- Source order (which rule appears last)
- Origin of the style (user agent, user styles, author styles)
These layers help the browser sort out conflicts without guessing.
Understanding Specificity in the Cascade
Specificity is basically a scoring system that the browser uses to determine which rule is more specific — and therefore more important.
Here's a basic breakdown of how different selectors rank:
- Inline styles (like
style="max-width:90%") have the highest score. - ID selectors (
#header) come next. - Class selectors , attribute selectors, and pseudo-classes (
.btn,[type="text"],:hover) are lower. - Element selectors and pseudo-elements (
p,::before) are the lowest.
If two rules have the same specification, then the one that appears last in the stylesheet wins. This is called source order.
Also, if you're using something like !important , that throws a wrench into the normal flow — but we'll get to that in a bit.
Where Does !important Fit In?
Using !important is like shouting in a library — it gets attention, but it can make things messy.
When you add !important to a declaration:
p {
color: blue !important;
} It overrides other declarations regardless of specificity or source order , unless another !important rule with equal or higher specification comes later.
This can be useful in some cases — like overriding third-party styles — but overusing it leads to hard-to-maintain code. It skips the usual cascade logic, making debugging trickier.
Use it sparingly, and only when absolutely necessary.
Practical Tips for Managing the Cascade
Here are a few real-world strategies to avoid getting tripped up by the cascade:
- Keep your CSS organized — group related styles together and avoid scattered overrides.
- Use consistency naming conventions (like BEM) to manage specificity without going overboard.
- Avoid
!importantunless you're dealing with external libraries or inline styles. - Use browser dev tools to inspect which styles are being applied — they show you exactly what's winning and why.
You'll start noticing patterns once you get used to how the cascade behaves. And that makes styling a lot smoother.
Cascade might sound complex at first, but it's really just a system for resolving style conflicts. Once you understand specificity, source order, and the role of !important , it becomes much easier to predict and control how your styles behave.
Basically that's it.
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