Custom syntax highlighting for Gatsby

April 14, 2018

I wanted to add compile-time syntax highlighting to the code sections of this blog today, so I took a look around.

I was already using gatsby-transformer-remark for markdown to HTML conversion of blog posts, so I needed to add a plugin that would parse my code blocks into styleable html. Enter the handy Gatsby plugin gatsby-remark-prismjs, it was super simple to configure for use with gatsby-transformer-remark. I only needed to add it as a plugin in my Gatsby config

// In your gatsby-config.js change this simple include:
plugins: [

// to this 'configured' include:
plugins: [
    resolve: 'gatsby-transformer-remark',
    options: {
      plugins: [ 'gatsby-remark-prismjs' ]

Congratulations, you now have annotated, but unstyled, code blocks.

Now we need to include some CSS to apply some colors to our marked-up syntax. PrismJS has plenty of excellent, standard themes, but I wanted some simpler. It needed to be easily readable without being too jarring or removed from the style and theme of this site, so I looked around for something simple to extend.

MoOx/sass-prism-theme-base by MoOx was a great base to build off of. The repo wasn’t easily consumable by yarn, so I copied the _prism.scss for the base styles into my project to be used there. I may need to investigate sharing a variant of a base SASS PrismJS theme, as that’s exactly what I was looking for.

I created a base _syntax-theme.scss file to contain my variables and setting overrides, it looks a little like this:

// _syntax-theme.scss
$code:     #454390;
$value:    #e6d06c;
$keyword:  #f12769;
$operator: #f00;
$subtle:   #aaa;
$comment:  #999;

$code-color:         $code;
$code-color-fade:    $subtle;
$code-color-comment: $comment;
$code-color-keyword: $keyword;
$code-color-value:   $code;
$code-color-string:  $value;

$code-tab-size:      2;
$code-font-size: 	   18px;
$code-line-height:	 1.7;

@import "prism";

I hope this quick explanation helps get some more people out there blogging about code.