CSS Selectors and Specificity

When you are applying more than one style to your web page on the same element, it is difficult to find out which one takes precedence. You can figure it out using CSS selector specificity and priority. In this complete guide to specificity in CSS, we will discuss what CSS selectors and CSS specificity are, and how they work.

Table of Contents:

• What are CSS Selectors?
• Types of CSS Selectors with Examples
• What is CSS Specificity?
  • Understanding How CSS Specificity Works
• CSS Specificity Hierarchy: Inline, ID, Class, and Element
  • CSS Specificity Calculation Example with Code
• Using the !important Rule to Override CSS Styles
• What Makes a CSS Selector More Specific?
• Best Practices to Avoid CSS Specificity Conflicts
• How to Debug CSS Specificity Problems in Your Stylesheet
• Real-World Scenarios of CSS Conflicts
• Conclusion

What are CSS Selectors?

CSS selectors are used to select the HTML elements that you want to style.  They tell the browser which elements to style and how to style them based on tags, classes, IDs, attributes, or relationships in the HTML. Understanding the CSS selectors is the first step to learn and understanding about CSS selector specificity and priority.

Types of CSS Selectors with Examples

There are different types of CSS selectors, which are:

• Universal Selector: It selects the whole document. (e.g., *)
• Element selector: It selects all elements of one type. (e.g., h1, p)
• Class selector: It selects elements with a specific class. (e.g., .title)
• ID selector: It selects an element with a specific ID. (e.g., #header)
• Attribute selector: It selects elements based on their attributes. (e.g., [type=”text”])
• Pseudo-class and pseudo-element selectors: It selects specific states or parts of elements (e.g., :hover, ::after)

What is CSS Specificity?

CSS specificity decides which style is applied when multiple selectors target the same element. It helps you find which style has taken charge. You can specify it based on the types of CSS selectors you were using. The higher the CSS specificity, the more important the style becomes.

Understanding How CSS Specificity Works

You can get various types of CSS selectors. You can calculate the CSS specificity of a selector based on a set of rules, which determine which style should take the highest priority. This explains how to calculate CSS specificity and how CSS selectors affect priority.

• Inline Styles: The element that got styled using the direct style tag gets the highest priority in CSS. You can see they always override styles in CSS, no matter where the other styles come from.

Example: 

   <p style="color: red;">This is a red paragraph.</p>

• ID selectors: Compared to the class or element selectors, the ID selector has the highest CSS specificity. It applies when multiple styles apply to the same element. This highlights the difference between ID and class specificity in CSS.

Example:

   #main-title {
    color: blue;
   }

• Class, Attribute, and Pseudo-Class Selectors: These CSS selectors have fewer ID selectors but are more specific than element selectors. It lies in the middle when determining the style’s priority.
  
• Element and Pseudo-Element Selectors: The least specific CSS selectors.

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CSS Specificity Hierarchy: Inline, ID, Class, and Element

Let’s see how the CSS specificity hierarchy works, demonstrating how CSS selectors affect priority. This forms the core of specificity in CSS.

• Inline styles (added using the style attribute) score 1000, giving them the highest CSS priority.
• ID selectors (like #id): Score 100, giving them high priority but less than inline styles.
• Class, attribute, and pseudo-class selectors (like .class, [attr], and:hover) score 10, placing them in the middle of CSS specificity.
• Element and pseudo-element selectors (like h1, ::before): Score 1, giving them the least CSS priority.

CSS Specificity Calculation Example with Code

h1 { color: black; }		/* Specificity: 1 */
.title { color: blue; }		/* Specificity: 10 */
#main-title { color: red; }	/* Specificity: 100 */

When you apply these three styles to the h1, the text color turns red because it has the highest specificity. 

Using the !important Rule to Override CSS Styles

You can use !important in a style declaration to override styles in CSS, all others without considering their specificity. 

Example:

p {
  color: blue !important;
}

This rule even overrides the inline style. If you find another element with !important, then the element with the highest specificity takes first priority. However, using !important CSS extensively is generally discouraged in best practices for HTML hyperlinks.

What Makes a CSS Selector More Specific?

A CSS selector becomes more specific when it includes IDs, classes, attributes, or element names. The more specific the CSS selector, the higher its CSS priority when styles conflict. An ID selector (#id) is more specific than a class (.class) or element (div). Adding more CSS selectors like div.content p increases specificity. Inline styles and !important rules can override normal specificity. Understanding this helps prevent styling conflicts in complex CSS.

Best Practices to Avoid CSS Specificity Conflicts

Following these best practices for HTML hyperlinks helps to manage specificity in CSS and prevent conflicts.

• Stick to Simpler Selectors: You can use class selectors instead of IDs.
• Avoid Too Much Nesting: You can avoid over-nesting selectors since it makes them unnecessarily specific and harder to manage their CSS priority.
• Use !important only when necessary: You can avoid overusing it because it may cause many bugs in the code and make it hard to override styles in CSS predictably.
• Keep a Style Guide: A well-organized CSS prevents problems, and you can get clean code.
• Apply CSS Resets or Normalize.css: You can use it to remove browser inconsistencies.
• Follow a Naming Convention: You can follow methods like BEM (Block Element Modifier) to help in CSS management.
• Use CSS Variables: You can use variables to simplify the repeated styles and reduce the problems related to CSS specificity. 

How to Debug CSS Specificity Problems in Your Stylesheet

Here are some strategies to debug CSS specificity-related problems, particularly understanding how CSS selectors affect priority:

1. Use Developer Tools: Use browsers like Chrome and Firefox, which have “Inspect Element” tools for reviewing the applied styles directly.

2. Check Computed Styles: You can use the “Computed” tab in dev tools to show the final styles that apply to an element.

3. Use Online Specificity Calculators: Use the Specificity Calculator to help you figure out selector weights and solve the conflicts.

4. Refactor CSS: Reorganize the stylesheet if you face an issue regarding the CSS specificity. 

Real-World Scenarios of CSS Conflicts

Understanding these scenarios helps illustrate the importance of CSS specificity and CSS priority in real applications.

1. Multiple Styles Target the Same Element: Two rules (e.g., a class and an ID) try to style the same element, but the one with higher specificity wins.
2. Overuse of !important: Using !important in many places makes it hard to override styles in CSS and leads to messy code.
3. Third-Party Styles Overriding Yours: Frameworks like Bootstrap may apply styles that override your custom CSS.
4. Conflicting Media Queries: Overlapping media queries may apply unexpected styles on certain screen sizes.
5. Deeply Nested CSS Selectors: Using long selector chains (e.g., div ul li a span) makes it difficult to override styles in CSS without increasing specificity.
6. Inline Styles vs. External Stylesheets: Inline styles take precedence over CSS rules in stylesheets, which can cause confusion due to their very high CSS priority.
7. Missing or Duplicate Class Names: Elements with similar class names may accidentally share styles or get the wrong ones.
8. Global Styles Affecting Local Components: Styles meant for the entire site may accidentally override styles inside specific components or sections.

Conclusion

Specificity in CSS determines the priority of the styles when many styles have been applied to the elements. The inline styles have the highest CSS priority (1000), followed by ID selectors (100), class/attribute/pseudo-class selectors (10), and element/pseudo-element selectors (1). You can also use !important CSS to override styles in CSS and all the specificity rules. You can avoid the issues related to CSS specificity, and you can depend on the class selectors, avoid over-nesting, and avoid overusing !important. 
If you’re getting ready for a job, explore these CSS interview questions. 

Understanding CSS Selector Priority/Specificity – FAQs