Using CSS 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 countercounter-increment - Increments a counter valuecontent - Inserts generated contentcounter() or counters() function - Adds the value of a counter to an elementTo 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) ": ";
}
Try it Yourself
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) " ";
}
Try it Yourself
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,".") " ";
}
Try it Yourself
| 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 |