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A Guide to CSS counter

samanthaming profile image Samantha Ming ・5 min read

A Guide to CSS counter

Code Tidbit by SamanthaMing.com

Use the "counter" property to turn any element into a numbered list. Similar to how the ordered list tag works <ol>. Very useful if you're creating a documentation site where you need to automatically number the headings or create a table of contents 👍

div {
  /* Define & Initialize Counter */
  counter-reset: tidbit-counter;
}

h2::before {
  /* Increment Counter */
  counter-increment: tidbit-counter;

  /* Display Counter */
  content: counter(tidbit-counter) ": ";
}
<div>
  <h2>HTML</h2>
  <h2>CSS</h2>
  <h2>JS</h2>
</div>

How the counter property work

There are 3 steps to get the counter to work:

  1. Define & Initialize Counter
  2. Increment Counter
  3. Display Counter

1. Define & Initialize Counter

There are 2 parts to this step. You need to define your counter and give it a name.

1a. Define Counter
I have named mine tidbit-counter. We give it a name so we can call it in the later steps.

counter-reset: tidbit-counter;

1b. Initialize Counter

The next part is to initialize your counter. By default, the value of this is 0. Note, this number is not displayed. This is just where you setting the "starting" of your counter. So if I had set this number to be 20, then my output would go 21, 22, 23...etc. Assuming that my increment is 1 (more on this later).

counter-reset Output
0 1, 2, 3 ...etc
20 21, 22, 23...etc
58 59, 60, 61...etc

Here's an example:

div {
  counter-reset: tidbit-counter 58; /* 👈 */
}

h2::before {
  counter-increment: tidbit-counter;
  content: counter(tidbit-counter) ": ";
}
<div>
  <h2>HTML</h2>
  <h2>CSS</h2>
  <h2>JS</h2>
</div>
59: HTML
60: CSS
61: JS

Where to apply the counter-reset property?

You want to apply the counter-reset property on the parent element. Here's what happens if you don't apply it to the parent.

/* ❌ Wrong */
h2 {
  counter-reset: tidbit-counter;
}

h2::before {
  counter-increment: tidbit-counter;
  content: counter(tidbit-counter) ": ";
}

And here's the output. As you noticed, it doesn't increment properly 🙁

1: HTML
1: CSS
1: JS

Also, it doesn't have to be the direct parent. As long as it's an HTML element that wraps your counter list. You're good. Like this:

<section>
  <div>
    <h2>HTML</h2>
    <h2>CSS</h2>
    <h2>JS</h2>
  </div>
</section>
/* ✅ This works */
section {
  counter-reset: tidbit-counter;
}
1: HTML
2: CSS
3: JS

2. Increment Counter

Once you set up your counter. Now you can start incrementing it. Here's the syntax for this property:

counter-increment: <counter name> <integer>

As you noticed, it accepts an integer argument. That means you are not restricted to just increasing the counter value by 1. Below chart assumes counter-reset is 0.

counter-increment Output
1 (default) 1, 2, 3 ...etc
5 5, 10, 15...etc
-5 -5, -10, -15...etc

And yes, you can also pass in a negative integer to decrease the counter. Okay, let's see how that would be implemented:

div {
  counter-reset: tidbit-counter;
}

h2::before {
  counter-increment: tidbit-counter -5; /* 👈 */
  content: counter(tidbit-counter) ": ";
}
<div>
  <h2>HTML</h2>
  <h2>CSS</h2>
  <h2>JS</h2>
</div>
-5: HTML
-10: CSS
-15: JS

3. Display Counter

Finally, to display the counter, we need to pass the counter function as the value for our content property. The content property is often the way for us to display value in our HTML through CSS. Here's the syntax for our counter function.

counter(<counter name>, <counter list style>)

By default, we have been working numbers. And that's the default counter list style or in the docs, they call it style. But you can also pass in other styles.

style Output
default 1, 2, 3 ...etc
upper-alpha A, B, C ...etc
lower-roman i, ii, iii ...etc
thai ๑, ๒, ๓ ...etc

You can see the full list of styles here

And let's look at an example:

div {
  counter-reset: tidbit-counter;
}

h2::before {
  counter-increment: tidbit-counter;
  content: counter(tidbit-counter, thai); /* 👈 */
}
<div>
  <h2>HTML</h2>
  <h2>CSS</h2>
  <h2>JS</h2>
</div>
๑HTML
๒CSS
๓JS

Multiple Counters

You can also set multiple counters just by simply defining another counter name.

div {
  counter-reset: counter-one counter-two 100; /* 👈 */
}

h2::before {
  counter-increment: counter-one;
  content: counter(counter-one) ": ";
} 

h3::before {
  counter-increment: counter-two;
  content: counter(counter-two) ": ";
}
<div>
  <h2>one</h2>
  <h2>one</h2>

  <h3>two</h3>
  <h3>two</h3>
</div>
1: one
2: one

101: two
102: two

Nested Counter

You can also set a nested counter. Instead of using counter, you use the plural form counters. The counters accept an additional argument:

counter(<counter name>, <string>, <counter list style>)

The string argument is a string separator that you use to indicated how you want to separate the list item for nested counters.

string Output
"." 1.1, 1.2, 1.3 ...etc
">" 1>1, 1>2, 1>3 ...etc
":" 1:1, 1:2, 1:3 ...etc

Let's look at an example:

div {
  counter-reset: multi-counters;
}

h2::before {
  counter-increment: multi-counters;
  content: counters(multi-counters, ".") ": ";
} 
<div>
  <h2>Frameworks</h2>
  <div>
    <h2>Vue</h2>
    <h2>React</h2>
    <h2>Angular</h2>
  </div>
</div>
1: Frameworks
  1.1: Vue
  1.2: React
  1.3: Angular

counter vs <ol>

CSS counter doesn't replace <ol>. If you have a numbered ordered list, then you should absolutely still use <ol> because it's important that you structure your HTML using the proper semantics. Semantic markup is crucial for Accessibility and SEO.

<ol> for the win

Here's an example where I should use <ol>. In this instance, I'm just listing a bunch of rules. It makes semantic sense to use an ordered list <ol>.

<h2>Rules</h2>

<ol>
  <li>You do not talk about Fight Club</li>
  <li>You do not talk about Fight Club</li>
</ol>

CSScounter for the win

Here's an example where I would use CSS counter. In this instance, I have a documentation page using headings h2 and paragraphs p. In this example, having a counter is more of a visual presentation. This example would make sense using CSS counter.

<article>
  <h2>What is Vue.js?</h2>
  <p>Vue is a progressive framework for building user interfaces.</p>

  <h2>Getting Started</h2>
  <p>Visit Vuejs.org to learn more!</p>
</article>
1: What is Vue.js?
Vue is a progressive framework for building user interfaces.

2: Getting Started
Visit Vuejs.org to learn more!

☝️Can you tell I really like Vue.js 😝


Browser Support

The CSS counter is supported by all major browsers including Internet Explorer 8 and above.

Can I Use: CSS Counters


Resources


Thanks for reading ❤
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Discussion

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acostalima profile image
André Costa Lima

I didn't even know you could control list numbering with CSS and make elements to behave like ol 😮

Thanks! 👌

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samanthaming profile image
Samantha Ming Author

I know, it's pretty sweet! There are so much cool things CSS can tweak. I'll make sure to share if I find more 😊

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islam profile image
Islam Sayed

I talked about your article as the first one of my 150 articles challenge here: Article # 1 of 150: A Guide To CSS Counter.

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samanthaming profile image
Samantha Ming Author

That’s super cool, thanks! But I don’t think the link is working for me 🤔

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islam profile image
Islam Sayed

This is totally new to me. Thank you so much. 💚

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samanthaming profile image
Samantha Ming Author

You're welcome! Thanks for reading it 😊

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devworkssimone profile image
DevWorksSimone

I think you meant to writer
counter-increment:
Instead of
counter-reset:
In action 2.Increment-counter.
Stile Reading seems interesting

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samanthaming profile image
Samantha Ming Author

Ugh yes 😱I'll fix it now, thank you!!!

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kozakrisz profile image
Krisztian Kecskes

Thank you Samantha! Useful article as always! :D

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samanthaming profile image
Samantha Ming Author

Awesome, glad to hear it was helpful! Thanks for reading the article 😄