Style guide

Key principle

Highlight.js themes are language agnostic.

Instead of trying to make a rich set of highlightable classes look good in a handful of languages we have a limited set of classes that work for all languages.

Hence, there are two important implications:

  • Highlight.js styles tend to be minimalistic.
  • It’s not possible to exactly emulate themes from other highlighting engines.

Defining a theme

A theme is a single CSS defining styles for class names listed in the class reference. The general guideline is to style all available classes, however an author may deliberately choose to exclude some (for example, .attr is usually left unstyled).

You are not required to invent a separate styling for every group of class names, it’s perfectly okay to group them:

.hljs-string,
.hljs-section,
.hljs-selector-class,
.hljs-template-variable,
.hljs-deletion {
  color: #800;
}

Use as few or as many unique style combinations as you want.

Typography and layout dos and don’ts

Don’t use:

  • non-standard borders/margin/paddings for the root container .hljs
  • specific font faces
  • font size, line height and anything that affects position and size of characters within the container

Okay to use:

  • colors (obviously!)
  • italic, bold, underlining, etc.
  • image backgrounds

These may seem arbitrary at first but it’s what has shown to make sense in practice.

There’s also a common set of rules that has to be defined for the root container verbatim:

.hljs {
  display: block;
  overflow-x: auto;
  padding: 0.5em;
}

.subst

One important caveat: don’t forget to style .subst. It’s used for parsed sections within strings and almost always should be reset to the default color:

.hljs,
.hljs-subst {
  color: black;
}

Contributing

You should include a comment at the top of the CSS file with attribution and other meta data if necessary. The format is free:

/*

Fancy style (c) John Smith <email@domain.com>

*/

If you’re a new contributor add yourself to the authors list in AUTHORS.*.txt (use either English and/or Russian version). Also update CHANGES.md with your contribution.

Send your contribution as a pull request on GitHub.