Source Highlighting Themes

You can apply a bundled source highlighter theme to your source blocks or define and apply your own.

Using a bundled highlighting theme

Rouge bundles several themes you can use to colorize your source blocks. To use one of these themes, first set the value of the source-highlighter document attribute to rouge. Then, specify the desired theme using the rouge-style document attribute.

The following example demonstrates how to apply the monokai theme from Rouge to source blocks.

= Document Title
:source-highlighter: rouge
:rouge-style: monokai

You can generate a list of all available themes by running the following command:

$ ruby -e 'require :rouge.to_s; puts Rouge::Theme.registry.keys.sort.join ?\n'

If the bundled themes don’t suit your needs, you can define one of your own.

Define a custom highlighting theme

A custom theme for Rouge is defined using a Ruby class. Start by creating a Ruby source file to define your theme. Name the file according to the name of your theme and put the file in a folder of your choice (e.g., rouge_themes/custom.rb). The name of the Ruby class doesn’t matter, though it’s customary to name it according to the name of the theme as well.

require 'rouge' unless defined? ::Rouge.version

module Rouge; module Themes
  class Custom < CSSTheme
    name 'custom'

    style Comment,           fg: '#008800', italic: true
    style Error,             fg: '#a61717', bg: '#e3d2d2'
    style Str,               fg: '#0000ff'
    style Str::Char,         fg: '#800080'
    style Num,               fg: '#0000ff'
    style Keyword,           fg: '#000080', bold: true
    style Operator::Word,    bold: true
    style Name::Tag,         fg: '#000080', bold: true
    style Name::Attribute,   fg: '#ff0000'
    style Generic::Deleted,  fg: '#000000', bg: '#ffdddd', inline_block: true, extend: true
    style Generic::Inserted, fg: '#000000', bg: '#ddffdd', inline_block: true, extend: true
    style Text, {}
end; end

Each style declaration accepts the following properties:

  • fg - sets the foreground (text) color

  • bg - sets the background color

  • bold - change the font weight to bold

  • italic - change the font style to italic

  • underline - add an underline to the text

  • inline_block - fill the background color to the height of the line (Asciidoctor PDF only)

  • extend - extend the background color to the end of the line for a line-oriented match (Asciidoctor PDF only)

Colors are defined using hexadecimal format (e.g., #ff0000 for red).

Use the Text token to set the background color of the source block and the default text color.

The complete list of tokens can be found in the token.rb file from Rouge. Refer to the bundled themes to find more examples.

Once you’ve defined your theme, you need to enable it to use it using the rouge-style document attribute, which you specify in the document header or via the Asciidoctor CLI or API.

= Document Title
:source-highlighter: rouge
:rouge-style: custom

Finally, you need to activate your theme by requiring the theme file when you invoke Asciidoctor.

$ asciidoctor -r ./rouge_themes/custom.rb sample.adoc

You should now see that the source code is highlighted to your liking. For more information about source highlighting with Rouge, refer to the Rouge project page.