As you write more and more code, you might observe that more than one CSS rule can be applied to an element.

By mistake, you can also double-style an element. In that case, which rule will be applied?

For situations where conflict arises, CSS applies a set of rules and rank them in a specificity hierarchy and apply the 'winner'.

Specificity Hierarchy

There are 4 categories for this hierarchy:

1. Inline styles
This looks and operates much like CSS, but with a few differences. Inline styles affect the tag they are written in directly, without the use of selectors, which are needed in CSS.

/*example*/
<p style="color: green">

2. IDs
This type of selector matches an element from your code depending on the value of the ID selector.

/*HTML*/
<div id="footer">Contact me</div>

/*CSS*/
#footer {
   display: flex;
}

3. (Pseudo-)classes & attributes
A pseudo-class is used to define a special state of an element such as active, focus, visited, hover and so on.

/*when the link is clicked*/
a:active {
   color: pink;
}

A class would be defined just as the ID selector, with the difference that its value would be based on the class selector.

/*HTML*/
<div class="container">Hello</div>

/*CSS*/
.container {
   font-size: 2rem;
}

You can also style your HTML elements that have a specific attributes or attribute values.

/*HTML*/
<a href="https://website1.com">Website 1</a>
<a href="http://website2.com" target="_blank">Website 2</a>

/*CSS*/
a[target] {
   background-color: blue;
}

4. (Pseudo-)elements
CSS pseudo-elements are used to style specified parts of an element.

h1::first-letter {
  font-weight: 900;
}

On the other hand, elements can be styled as simple as they come in your HTML structure.

h3 {
   border-radius: 10px;
}

Calculate Specificity

1. Start at 0
2. Add 1000 for each inline style (this always has the highest priority - using the !important rule will override the inline style)
3. Add 100 for each ID value
4. Add 10 for each (pseudo-)class or attribute value
5. Add 1 for each (pseudo-)element value.

Example

h1.p -> 1 + 10 -> 11
h1#title -> 1 + 100 -> 101
<h1 style="color: red"> -> 1000 -> 1000

Want to see more examples and have some exercises?
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Cover photo by Afif Ramdhasuma on Unsplash