::highlight()

Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The ::highlight() CSS pseudo-element applies styles to a custom highlight.

A custom highlight is a collection of Range objects and is registered on a webpage using the HighlightRegistry.

Allowable properties

Only certain CSS properties can be used with ::highlight():

In particular, background-image is ignored.

Syntax

::highlight(custom-highlight-name)

Examples

Highlighting characters

HTML

html

<p id="rainbow-text">CSS Custom Highlight API rainbow</p>

CSS

css

#rainbow-text {
  font-family: monospace;
  font-size: 1.5rem;
}

::highlight(rainbow-color-1) {
  color: #ad26ad;
  text-decoration: underline;
}
::highlight(rainbow-color-2) {
  color: #5d0a99;
  text-decoration: underline;
}
::highlight(rainbow-color-3) {
  color: #0000ff;
  text-decoration: underline;
}
::highlight(rainbow-color-4) {
  color: #07c607;
  text-decoration: underline;
}
::highlight(rainbow-color-5) {
  color: #b3b308;
  text-decoration: underline;
}
::highlight(rainbow-color-6) {
  color: #ffa500;
  text-decoration: underline;
}
::highlight(rainbow-color-7) {
  color: #ff0000;
  text-decoration: underline;
}

JavaScript

js

const textNode = document.getElementById("rainbow-text").firstChild;

if (!CSS.highlights) {
  textNode.textContent =
    "The CSS Custom Highlight API is not supported in this browser!";
}

// Create and register highlights for each color in the rainbow.
const highlights = [];
for (let i = 0; i < 7; i++) {
  // Create a new highlight for this color.
  const colorHighlight = new Highlight();
  highlights.push(colorHighlight);

  // Register this highlight under a custom name.
  CSS.highlights.set(`rainbow-color-${i + 1}`, colorHighlight);
}

// Iterate over the text, character by character.
for (let i = 0; i < textNode.textContent.length; i++) {
  // Create a new range just for this character.
  const range = new Range();
  range.setStart(textNode, i);
  range.setEnd(textNode, i + 1);

  // Add the range to the next available highlight,
  // looping back to the first one once we've reached the 7th.
  highlights[i % 7].add(range);
}

Result

Specifications

Specification
CSS Custom Highlight API Module Level 1
# custom-highlight-pseudo

Browser compatibility

BCD tables only load in the browser