variables.md

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Variables

We may assign expressions to variables and use them throughout our stylesheet:

 font-size = 14px

 body
   font font-size Arial, sans-serif

 //Compiles to:
 body {
   font: 14px Arial, sans-serif;
 }

Variables can even consist of an expression list:

font-size = 14px
font-stack = "Lucida Grande", Arial, sans-serif

body
  font font-size font-stack

//Compiles to:
body {
  font: 14px "Lucida Grande", Arial, sans-serif;
}

Identifiers (variable names, functions, etc.) may also include the $ character. For example:

$font-size = 14px
body {
  font: $font-size sans-serif;
}

We can not use null to create empty variable, but parentheses () can do that:

empty = ()
body {
  font: empty sans-serif;
}

//Compiles to:
body {
  font: sans-serif;
}

Property Lookup

Another cool feature unique to Stylus is the ability to reference properties defined without assigning their values to variables. A great example of this is the logic required for vertically and horizontally center an element (typically done using percentages and negative margins, as follows):

 #logo
   position: absolute
   top: 50%
   left: 50%
   width: w = 150px
   height: h = 80px
   margin-left: -(w / 2)
   margin-top: -(h / 2)

Instead of assigning the variables w and h, we can simply prepend the @ character to the property name to access the value:

 #logo
   position: absolute
   top: 50%
   left: 50%
   width: 150px
   height: 80px
   margin-left: -(@width / 2)
   margin-top: -(@height / 2)

Another use-case is conditionally defining properties within mixins based on the existence of others . In the following example, we apply a default z-index of 1—but only if z-index was not previously specified:

  position()
    position: arguments
    z-index: 1 unless @z-index

  #logo
    z-index: 20
    position: absolute

  #logo2
    position: absolute

Property lookup will "bubble up" the stack until found, or return null if the property cannot be resolved. In the following example, @color will resolve to blue:

  body
    color: red
    ul
      li
        color: blue
        a
          background-color: @color