anchor.diff:  ----
   base:
     font_color: #ff0000
  +----
  +
  +It's also possible to specify no color by assigning the special value `transparent` as shown here:
  +
  +[source,yaml]
  +----
  +base:
  +  background_color: transparent
   ----
   
   ==== RGB
  
positive.code: The theme language supports color values in three formats:
  
  Hex:: A string of 3 or 6 characters with an optional leading `#`.
  RGB:: An array of numeric values ranging from 0 to 255.
  CMYK:: An array of numeric values ranging from 0 to 1 or from 0% to 100%.
  
  
negative.code:   font_size_small: $base_font_size * 0.85
  ----
  
  We'll cover more about math expressions later.
  
  ==== 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.
  If you are going to do this, it's recommended that you organize the keys under a custom namespace, such as `brand`.
  
  For instance, here's how you can define your (very patriotic) brand colors:
  
  [source,yaml]
  ----
  brand:
    red: #E0162B
    white: #FFFFFF
    blue: #0052A5
  ----
  
  You can now use these custom variables later in the theme file:
  
  [source,yaml]
  ----
  base:
    font_color: $brand_blue
  ----
  
  === Math expressions & functions
  
  