CSS Counters

CSS counters are similar to variables. These are maintained by CSS and those values can be incremented by CSS rules to track how many times they are used.

CSS counters facilitate simple CSS based incrementing and display of a number for generated content.

CSS Counter Properties

Property	Description
content	Used with the ::before and ::after pseudo-elements, to insert generated content
counter-increment	Increments one or more counter values
counter-reset	Creates or resets one or more counters
counter()	Returns the current value of the named counter

note

Before using a CSS counter, it must be created with counter-reset.

Automatic Numbering With Counters

CSS counters are like "variables". The variable values can be incremented by CSS rules (which will track how many times they are used).

To work with CSS counters we will use the following properties:

• counter-reset - Creates or resets a counter
• counter-increment - Increments a counter value
• content - Inserts generated content
• counter() or counters() function - Adds the value of a counter to an element

To use a CSS counter, it must first be created with counter-reset.

The following example creates a counter for the page (in the body selector), then increments the counter value for each <h2> element and adds "Section <value of the counter>:" to the beginning of each <h2> element:

body {  
	counter-reset:  section;  
}  
  
h2::before {  
	counter-increment:  section;  
	content:  "Section " counter(section) ": ";  
}

<h2>Title</h2>
<h2>Title</h2>
<h2>Title</h2>
<h2>Title</h2>

Nesting Counters

The following example creates one counter for the page (section) and one counter for each <h1> element (subsection). The "section" counter will be counted for each <h1> element with "Section <value of the section counter>.", and the "subsection" counter will be counted for each <h2> element with "<value of the section counter>.<value of the subsection counter>":

body {  
	counter-reset:  section;  
}  
  
h1 {  
	counter-reset:  subsection;  
}  
  
h1::before {  
	counter-increment:  section;  
	content:  "Section " counter(section) ". ";  
}  
  
h2::before {  
	counter-increment:  subsection;  
	content:  counter(section) "." counter(subsection) " ";  
}

A counter can also be useful to make outlined lists because a new instance of a counter is automatically created in child elements. Here we use the counters() function to insert a string between different levels of nested counters:

ol {  
	counter-reset:  section;  
	list-style-type:  none;  
}  
  
li::before {  
	counter-increment:  section;  
	content:  counters(section,".") " ";  
}