Sunlight highlighter in GitBook

Sunlight is a context-aware, client-side syntax highlighter. It does as a good of a job as can be done highlighting code without performing static analysis.

Dark theme

Licensed under Apache License 2.0.

Note: Please check the section breaking changes if your old book does not build anymore.


  • Better syntax highlighting in some languages (but outdated in some others :-( )
  • Has different themes (“gitbook”, “light”, “dark”)
  • Line numbering
  • Per code block settings (demo here). It means you can select a different theme, line numbering, etc., in different code blocks.


You use Sunlight highlighter by adding the following in the book configuration:

    plugins: ["-highlight", "sunlight-highlighter"]

Note that you should disable the "highlight" plugin as well as enabling the "sunlight-highlighter" plugin. (In the GUI, an explicitly disabled plugin has a pale orange color.)

If you are using a non-default theme, or are using custom CSS, sunlight-highlighter may not show the correct output out-of-the-box. See the section Styling Sunlight highlighter to fix potential issues.


You can specify the following in the book configuration:

Option Default Valid values Description
theme "gitbook" any string Syntax highlighting theme. Themes "gitbook", "light" and "dark" are bundled with this plugin.
lineNumbers false false, true Whether to show line numbers

A sample configuration is shown below:

"pluginsConfig": {
  "sunlight-highlighter": {
    "theme": "dark",
    "lineNumber": true

Note: if you supplied any invalid configuration or malformed JSON, the book will cease to build.


Like the default syntax highlighter in GitBook, fenced code blocks are used in this plugin. However, not every language in highlight.js is supported. See below for the list of supported languages.


Dim x = 5
x = x ^ 2 + 1
Console.WriteLine("x = {0}", x)

Options in each code block

sunlight-highlighter allows setting options in the language info. The syntax is shown below:

// Your source code

The following options are now available (all case sensitive):

Option Description
theme The theme. gitbook, light and dark are bundled with this plugin.
lineNumbers Whether to show line numbers. Valid values are true and false.
lineNumberStart The line number of the first line. Can be any non-negative number. If not set, the value is 1.

Here is an example that highlight with the vb language, use the dark theme, and shows line numbers which starts from 100:

// Your source code

See the (demo) for more examples.

Setting options in plugin include-codeblock

The plugin include-codeblock imports source code from a file into your GitBook pages. Starting from version 3.1.1, the plugin is compatible with sunlight-highlighter 0.3.0 to enter options in the language string. See the (demo here).

Supported languages and language codes

Language Code
6502 assembler 6502asm
ActionScript actionscript
bash bash
Brainfuck brainfuck
C# csharp
C/C++ cpp
CSS css
Diff (unified and context) diff
DOS / Windows batch files batch
Erlang erlang
Haskell haskell
httpd (Apache config) httpd
Java java
JavaScript javascript
Lisp lisp
Lua lua
MySQL mysql
nginx nginx
Objective-C objective-c
Perl perl
PHP php
PowerShell powershell
Python python
Ruby ruby
Scala scala
T-SQL tsql
Visual Studio solution files (*.sln) sln
XML xml

In addition to the languages above, the following language code are available:

Code Function
plaintext No highlighting, but has theming and optionally add line numbers.
nohighlight Bypass the highlighter, i.e. no highlighting, no theming and no line numbers.
(nothing) Same as “nohighlight”.
any highlight.js language Maps to the corresponding sunlight language if supported (see above for the list).

Styling Sunlight highlighter

Dealing with non-default theme or custom CSS

The following CSS is added to Sunlight highlighter to fit into the style of GitBook:

.sunlight-code-container, .sunlight-line-number-margin {
    margin: -1em -1.1765em;
    padding: 1em 1.1765em;

This is done to offset the “0.85em 1em” padding created by GitBook. Code in GitBook is printed in 0.85em size, so we have 0.85/0.85 = 1(em) and 1/0.85 = 1.1765(em) in the offset code.

If you specify a different font size for the code, or is using a non-default theme, you should override these values with your own custom CSS. (It is sad that there is no all-in-one solution, and you need to make a different override for every different case.)

Note: margin-right and padding-right of .sunlight-line-number-margin are be further overridden.

Custom themes

Warning: the CSS for the themes will change in future versions.

To add a custom theme:

  1. Download a theme from (
  2. Edit the downloaded theme.
  3. The name of the theme must consist only of letters, digits, _ and -.
  4. Suppose the name of your theme is acme. Create a new LESS stylesheet as follows:
     .sunlight-theme-acme {
         @import (less) '[filename_of_your_theme.css]';
    For other theme names, replace acme by the name of your theme.
  5. Add your theme to your GitBook project:


  • Expose other configuration options in Sunlight highlighter.

Breaking changes

Version 0.4.0

  • The plugin option lineNumber in book.json is renamed to lineNumbers (was a misspell). This is done so the option name is the same everywhere.

Version 0.3.0

  • CSS are changed. Overrides of CSS older versions will not work.

Version 0.2.1

  • "default" theme (in 0.2.0) is renamed to "light".

  • The new default theme is "gitbook", which is essentially the "light" theme but with background color changed to #f7f7f7 (same as the color of GitBook code area). If you prefer the old theme in 0.2.0, you should switch to the "light" theme.

Known issues

  • When line numbers are used, the e-book/PDF outputs are not satisfactory.

Report bugs / Contributions

  • To report issues and request features for the GitBook plugin, post an issue in the GitHub repository
  • For Sunlight highlighter in general, refer to the links.


Setting Description Type Allowed values
lineNumbers Boolean
theme String
default = gitbook


Sunlight highlighter for GitBook. This highlighter produces better syntax highlighting than the default highlighter in some languages.

Latest: 0.4.3

0.1.0, 0.1.1, 0.1.2, 0.2.0, 0.2.1, 0.3.0, 0.4.0, 0.4.1, 0.4.2, 0.4.3,


0.4.3 >=3.0.0


Open on NPM