anchor.diff:  |pt (default)
   |===
   
  -. A percentage with the % unit is calculated relative to the width or height of the content area.
  +1. A percentage with the % unit is calculated relative to the width or height of the content area.
   Viewport-relative percentages (vw or vh units) are calculated as a percentage of the page width or height, respectively.
   Currently, percentage units can only be used for placing elements on the title page or for setting the width of a block image.
   
  
positive.code:   font-style: normal
  |===
  
  . The border is only used if a border color is specified and the border width is not explicitly set to 0.
  . The border offset is the amount that the background and border swells around the text.
  It does not affect the distance between the formatted phrase and the phrases that surround it.
  . The character sequence `%s` in the content key gets replaced with the button label.
  
  [#keys-key]
  === Key
  
negative.code:       size: 24
  |===
  
  1. The top and bottom padding values are ignored on admonition-label-padding.
  2. `<name>` can be `note`, `tip`, `warning`, `important`, or `caution`.
  All icon types must be grouped under a single `icons` category.
  In other words, _do not_ declare the `icons` category multiple times.
  The subkeys in the icon category cannot be flattened (e.g., `tip-name: far-lightbulb` is not valid syntax).
  3. Required.
  See the `.yml` files in the https://github.com/jessedoyle/prawn-icon/tree/master/data/fonts[prawn-icon repository] for a list of valid icon names.
  The prefix (e.g., `fas-`) determines which font set to use.
  If the prefix is not specified, `fa-` is assumed.
  