anchor.diff:  
   We'll cover more about math expressions later.
   
  -==== Custom variables
  +==== Custom Variables
   
   You can define arbitrary key names to make custom variables.
   This is one way to group reusable values at the top of your theme file.
  
positive.code: . The `toc_title` keys inherit from level-2 heading styles, except where noted.
  
  [#running-content]
  === Running header & footer
  
  The keys in this category control the arrangement and style of running header and footer content.
  
  
negative.code: The keys in this category control the size, margins and background of each page (i.e., canvas).
  
  NOTE: The background of the title page can be styled independently.
  See <<Title Page>> for details.
  
  [cols="3,4,5l"]
  |===
  