CSS Specificity

CSS specificity determines which rules apply to an element when multiple rules could apply. It is a measure of the importance of a selector in the cascade process.

Specificity Rules

Specificity is calculated based on the types of selectors used in the rule. It is typically expressed as a four-part value, like (a, b, c, d):

• a: Inline styles (e.g., style="color: red;") get a value of 1 in this column.
• b: Counts the number of ID selectors in the selector.
• c: Counts the number of class selectors, attributes selectors, and pseudo-classes.
• d: Counts the number of element selectors and pseudo-elements.

Specificity Calculation

Here’s how specificity is calculated:

1. Inline styles: Always have the highest specificity, represented by (1, 0, 0, 0).
2. ID selectors: Each ID selector increases the b component by 1.
3. Class selectors, attributes, and pseudo-classes: Each increases the c component by 1.
4. Element selectors and pseudo-elements: Each increases the d component by 1.

Examples

1. Inline Styles

   <div style="color: red;"></div>
   

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   Specificity: (1, 0, 0, 0)

2. ID Selector

   #main {
       color: blue;
   }
   

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   Specificity: (0, 1, 0, 0)

3. Class Selector

   .highlight {
       color: green;
   }
   

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   Specificity: (0, 0, 1, 0)

4. Element Selector

   p {
       color: black;
   }
   

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   specificity: (0, 0, 0, 1)

5. Combination

   #main .highlight p {
       color: orange;
   }
   

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   Specificity: (0, 1, 1, 1)

Overriding Specificity

1. More Specific Rule: A more specific rule will override a less specific rule.

   p {
       color: black;
   }
   .highlight p {
       color: green;
   }
   

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   The color of p inside .highlight will be green because .highlight p is more specific.

2. Order of Appearance: If two selectors have the same specificity, the one that appears last in the CSS will take precedence.

   p {
       color: black;
   }
   p {
       color: red;
   }
   

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   The color of p will be red because the second rule overrides the first one.

!important Rule: Adding !important to a declaration will override any other declarations, regardless of specificity.

p {
    color: black !important;
}
.highlight p {
    color: green;
}

1. The color of p will be black because !important takes precedence over normal specificity rules.

Practical Tips

• Use ID selectors sparingly to avoid overly specific rules that are hard to override.
• Use class selectors for reusable styles.
• Avoid using inline styles unless necessary as they have high specificity and can be difficult to override.
• Use !important sparingly as it makes debugging more challenging.

Understanding CSS specificity helps in writing efficient and manageable stylesheets, ensuring the right styles are applied to elements as intended.