Syntax highlighting: The look and feel

Nue uses the built-in syntax highlighter, Glow, to style your fenced code blocks with minimal setup. It offers the following features:

Design focused: Code blocks for languages like Markdown, YAML, TypeScript, Perl, SQL, and more, automatically match your design system’s colors.
Easy to use: Code blocks are styled by default. To align with your design system, just set 3-10 CSS variables.
Small footprint: The CSS for highlighting all languages is under 1 KB, including support for highlighted lines and regions.

For details on adding code blocks to your Markdown documents, refer to the code syntax guide. This article also explains how to adjust the look and feel of the generated HTML.

The HTML output

Syntax blocks are rendered as standard HTML tags, without additional class names. For example, the following Markdown block:

 ```javascript
^{// a comment}
 "A string value"
 ```

Produces the HTML:

<pre>
  <code language="javascript">
    <sup>^{// a comment}
    <em>"A string value"</em>
    ...
  </code>
</pre>

Built-in stylesheet

Whenever you add a syntax block, Nue includes a stylesheet for syntax highlighting. This stylesheet is configurable through CSS variables, and a few adjustments are usually all that’s needed to make code blocks match your design system:

^{/* Key Glow variables */}
pre {
  --glow-base-color: #eee;
  --glow-primary-color: #823;
  --glow-padding: 2em;
}

To disable the built-in stylesheet for full control over your styles, set this in site.yaml:

syntax_highlight: false

Then, add your own stylesheet with the variables and elements described below.

CSS variables and HTML elements

Below is a list of all CSS variables with the associated HTML elements for styling syntax blocks:

CSS variable	Default value	HTML tag	Description
accent-color	`#419fff`	strong	special emphasis
base-color	`#555`		foreground color
char-color	`#64748b`	i	brackets, commas...
comment-color	`#4e5d61`	sup	comments
counter-color	`#475569`		line numbers
del-color	`250, 110, 130`	del	deleted lines
error-color	`#ff0`	u	errors
ins-color	`50, 210, 190`	ins	inserted lines
line-color	`50, 180, 250`	dfn	highlighted lines
line-opacity	`0.15`		highlighted line opacity
padding	`1em`		container padding
primary-color	`#7dd3fc`	b	primary accent color
secondary-color	`#f472b6`	em	secondary accent color
selected-color	`#2dd4bf26`	mark	marked code
special-color	`#fff`	label	special standout words

Notes

Variables with no specific HTML element are applied to the root <pre> element.
If line numbers are enabled, each line is wrapped in a span, and the --glow-line-number variable applies to the span:before pseudo-element.
Highlighted row colors are specified in RGB format for compatibility with CSS functions.

Language-specific styling

To apply language-specific tweaks, use the language attribute, as in:

[language="html"] {
  --glow-accent-color: green;
}

Adjusting formatting

Glow uses bolding with --glow-special-color, and other elements get styled by color alone. You can add formatting to any elements to fine-tune the syntax blocks. For example:

^{/* Bold all secondary syntax elements */}
pre em {
  font-weight: bold;
}