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Apr 15, 2018 - 2 minute read - Comments - Hugo Not Security

Adding Custom Chroma Styles to Hugo Themes

Update: Chroma now supports solarized-dark families. Currently, this version is not used in Hugo.

Hugo has switched to Chroma for syntax highlighting from Pygments. While it still supports Pygments, it appears Chroma is much faster. However, Chroma does not support the solarized dark theme that is used by Hugo-Octopress. So I had to generate the CSS and add it manually.

The process is decently simple because Chroma has a built-in tool for converting styles _tools/style.py. You can see the files inside my clone:

Instructions

These steps are for an Ubuntu 16 machine, but can be adapted for any OS.

  1. Install Go, configure GOPATH and the rest.
  2. Install Chroma with go get github.com/alecthomas/chroma.
  3. Install Python 3.
  4. Install Pygments for Python 3: sudo apt-get install python3-pygments.
  5. Install Pystache for Python 3: sudo apt-get install python3-pystache.
  6. Clone solarized dark: git clone https://github.com/john2x/solarized-pygment/ (do not need to install it).
  7. (Optional) Rename the three py files inside solarized=pygment/pygments_solarized to more descriptive names. For example dark.py might become solarized-dark.py.
  8. Open each of them and note the style class name. For example for dark.py it’s SolarizedDarkStyle.
  9. Copy the files to the pygments installation path. On my machine it was:
    • /usr/local/lib/python3.5/dist-packages/Pygments-2.2.0-py3.5.egg/pygments/styles.
  10. Use the _tools/style.py to generate go files from styles:
    • python3 style.py [style-name] pygments.styles.[py-file-name].[style-class-name] > style-name.go
      • style-name is a string with new style’s name. E.g. solarized-dark.
      • py-file-name is the name of the py file (w/o extension) that was copied to the Pygments directory. E.g. dark.
      • style-class-name is the name of the python class inside the style. E.g. SolarizedDarkStyle.
  11. My example command was:
    • python3 style.py solarized-dark pygments.styles.dark.SolarizedDarkStyle > solarized-dark.go
  12. Repeat for any other styles.
  13. Copy the resulting go files to $GOPATH/Go/src/github.com/alecthomas/chroma/styles.
    • You can open the file to double-check the style name passed to chroma.MustNewStyle:
    • var SolarizedDark = Register(chroma.MustNewStyle("solarized-dark", chroma.StyleEntries{
  14. Now create the following Go application (or copy createCSS.go). Modify the file and style names as needed and execute it:

    createCSS.go
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    package main
    
    import (
        "os"
    
        "github.com/alecthomas/chroma/formatters/html"
        "github.com/alecthomas/chroma/styles"
    )
    
    func main() {
        f, _ := os.Create("solarized-dark.css")
        defer f.Close()
    
        formatter := html.New(html.WithClasses())
        if err := formatter.WriteCSS(f, styles.Get("solarized-dark")); err != nil {
            panic(err)
        }
    }

  15. Copy/paste the CSS files to your theme’s CSS.

  16. Inside your site’s config file:

    • Remove pygmentsUseClassic: This will tell Hugo to use Chroma.
    • pygmentsuseclasses = true: Use CSS for highlighting.
    • pygmentscodefences = true: This adds code highlight to code fences.