Understand Cascading and Flow of Styles in CSS

When we work with CSS, one of the fundamental concepts is to understand how styles are applied to a web page. The "cascade" is precisely the mechanism that defines how browsers decide which CSS rules to apply when there are multiple styles for the same element. Understanding the flow of styles and how cascading works not only improves our skills as developers, but also helps us write cleaner, more efficient and maintainable CSS code.

What is Waterfall in CSS?

Cascading is the process CSS uses to determine which styles to apply to elements on a page. This process follows certain rules and priorities based on three main factors:

1. Specificity: How specific the selector is.

2. Importance: Whether the !important property has been applied.

3. Declaration order: The place where the rule is located in the style sheet.

The waterfall evaluates these rules in order to decide which style should be applied. If two rules have the same level of specificity and neither uses !important, the browser will apply the rule that is closest to the end of the style sheet, following the order of the declaration.

How Style Flow Works

Style flow in CSS refers to the order in which style rules are applied depending on their specificity and location. Let's break down the most important points:

• Browser styles: All browsers apply certain styles by default (such as the margin on the body element or the unordered list ul ). These styles are applied first and can be overridden with our custom CSS rules.

• External styles: Those that we define in external style sheets, usually linked with the link tag in the HTML. These styles have higher priority than browser styles.

• Inline styles: These are styles applied directly in the HTML with the style attribute. They have higher specificity and usually override external style sheet rules.

• Rules !important: Using !important gives a rule the highest priority, overriding any other applied styles, regardless of specificity.

Basic Waterfall Example

Let's imagine an element with several rules applied from different places:

HTML

Suppose we have the following rules in our CSS

CSS

In this case, the text will appear blue, since cascade is the last defined declaration, in addition to having the same specificity as the previous declaration.

But you can come across this scenario, that although the specificity and the cascade are the same, you will be able to see a significant change.

CSS

In this case, the text will appear green, since the rule color: green !important; has the highest priority thanks to the use of !important, this ignores both specificity and cascade.

Declaration Order Example

As I mentioned before, if we have two rules with the same specificity but declared in different places, the one lower in the style sheet will apply:

The paragraph will be red, since that rule is declared after the rule that establishes the color black.

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Good Practices for Managing the Cascade and Flow of Styles

1. Minimize the use of !important: Although useful in specific situations, overusing !important can make your CSS difficult to maintain and overwrite. Use it only in cases where it is really necessary.

2. Use classes instead of IDs: Classes have less specificity than IDs, allowing more flexibility to override styles without generating overly specific CSS.

3. Organize your CSS from general to specific: Start by defining global styles and then move on to more specific rules. This follows a logical flow and makes the code easier to understand.

4. Group and order your selectors consistently: Keep rules that affect the same elements together to make it easier to visualize the waterfall and make adjustments.

5. Document the rules !important: If you need to use !important, document the reason. This will help you remember the reason and reduce the risk of the code getting confusing.

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Tools to Visualize Specificity and Cascade

There are online tools and browser extensions that allow you to visualize the specificity of your selectors and see the flow of styles applied to a particular element. For example:

• Chrome DevTools: By inspecting an element, you can see which CSS rules are being applied and in what order.

• Specificity Calculator: Tools like Specificity Calculator allow you to calculate the specificity of a selector.

• CSS Stats: A resource that allows you to view statistics of your CSS, including the level of specificity of your selectors.

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Summary

Cascading and flow of styles are basic principles in CSS, but understanding them well can make a big difference in how we organize and manage our styles. By knowing how cascading is applied, we can structure our CSS to be cleaner, more efficient, and easier to maintain.

Now that you understand cascading, you'll be able to have better control over your CSS styles and avoid unexpected overwrite issues!

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