Customize the Theme

Extend the default theme

A theme can extend another theme using the extends key. For example:

extends: default
  font-color: #FF0000

The extends key accepts either a single value or an array of values. Each value is interpreted as a filename. If the filename equals default, it resolves to the location of the default (built-in) theme. If the filename is absolute, it’s used as is. If the filename begins with ./, it’s resolved as a theme file relative to the current theme file. Otherwise, the filename is resolved as a theme file in the normal way (relative to the value of the pdf-themesdir attribute).

Currently, the theme starts out empty. Then, the files referenced by the extends key are loaded in order. Finally, the keys in the current file are loaded. Each time a theme is loaded, the keys are overlaid onto the keys from the previous theme.

Basic theme

Here’s an example of a basic theme file that extends the base theme:

extends: base
  layout: portrait
  margin: [0.75in, 1in, 0.75in, 1in]
  size: Letter
  font-color: #333333
  font-family: Times-Roman
  font-size: 12
  line-height-length: 17
  line-height: $base-line-height-length / $base-font-size
    font-style: italic
    text-decoration: line-through
    text-decoration-color: #FF0000
  font-color: #262626
  font-size: 17
  font-style: bold
  line-height: 1.2
  margin-bottom: 10
  font-color: #002FA7
  indent: $base-font-size * 1.5
  height: $base-line-height-length * 2.5
  line-height: 1
      content: '{page-number}'
      content: $footer-recto-right-content

When creating a new theme, you only have to define the keys you want to override from the extended theme, which is loaded prior to loading your custom theme. The converter uses the information from the theme map to help construct the PDF.

Basic extended theme

Instead of designing a theme from scratch, you can extend the default theme using the extends key as follows:

extends: default
  font-color: #FF0000

You can also point the extends key at another custom theme to extend from it. If you don’t want to extend any theme, including the base theme, omit the extends key or assign the value ~ to the extends key (i.e., extends: ~).

If the same theme appears multiple times in the theme hierarchy, it will only be loaded once by default. You can force the theme to be loaded, even if it has already been loaded, by adding the !important keyword at the end of the value offset by a space.

If you start a new theme from scratch, we strongly recommend defining TrueType fonts and specifying them in the base and codespan categories. Otherwise, Asciidoctor PDF will use built-in AFM fonts, which can result in missing functionality and warnings.

Instead of creating a theme from scratch, another option is to download the default-theme.yml file from the source repository. Save the file using a unique name (e.g., custom-theme.yml) and start hacking on it.

Alternatively, you can snag the file from your local installation using the following command:

$ ASCIIDOCTOR_PDF_DIR=`gem contents asciidoctor-pdf --show-install-dir`;\
  cp "$ASCIIDOCTOR_PDF_DIR/data/themes/default-theme.yml" custom-theme.yml