CSS Variable

By Xah Lee. Date: . Last updated: .

CSS allows you you use variable. This is called CSS custom property.

Declare variable like a property, but with the property name with prefix of 2 hyphens, like this:

--xx: red

Then, use it like this:

color: var(--xx)

Here's example.

something
<div class="xyz">something</div>
:root {
 --xx: pink;
 --yy: 2rem;
 --zz: solid thin red;
}

div.xyz
{
color: var(--xx);
font-size: var(--yy);
border: var(--zz);
}

The :root means root of the HTML or XML. You can also use html, but :root is better because in XML (example: SVG), the root is not html.

There must be no space after var.

Technically, CSS variable is called a CSS custom property. You should think of it as custom property, because, it is used just like properties, with the same cascading precedence for their scope, and overwriting a value is also the same as CSS cascade.

Browser Support

CSS custom property is supported by all major browsers since 2017 Jan, except Internet Explorer.

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CSS Basics

  1. Basics
  2. Tag Matching Tutorial
  3. Selector Syntax
  4. Units

Color

  1. Color Syntax
  2. Color Names
  3. Opacity
  4. Linear Gradient
  5. Radial Gradient

Font

  1. font-family
  2. Standard Web Fonts
  3. font-size
  4. Meaning of Font Size
  5. Font Weight
  6. Chinese Font Names

Box Model

  1. Border
  2. Outline
  3. Margin vs Padding
  4. Box Sizing

Layout

  1. Layout Tutorial
  2. Display Property
  3. Position: static, relative, fixed, absolute
  4. Pure CSS Table
  5. Tabbed Menu
  6. 3 Columns Page Layout
  7. Multi-Column Layout for Text Flow
  8. Fix Element to Window
  9. Centering
  10. Flowing List
  11. z-index
  12. Text Over Image
  13. Text Flow Around Image
  14. OverFlow, Scrollbar

Transform/Animation

  1. 2D Transform
  2. Transition
  3. Animation

Line Wrap, Justification

  1. Line Wrap
  2. Text Alignment, Justification
  3. Match first-letter and first-line
  4. “:before”, “:after”
  5. Text Decoration: Underline, Overline, Line-Through
  6. Letter Spacing, Word Spacing

Box Decoration

  1. Box Shadow
  2. Text Shadow
  3. Round Corners
  4. Background Image
  5. Image Rollover

Misc

  1. Computed Style
  2. Pseudo Class vs Pseudo Element
  3. Media Query
  4. Variable
  5. calc
  6. Reset
  7. user-select
  8. Data URI Scheme
  9. protocol-relative URL
  10. Default Unit
  11. Declaring Character Set in CSS File
  12. Jargons Explained: Tag, Element, Node, Object, Attribute, Property, Method
  13. Display Table on Small Screen
  14. Fixed Aspect Ratio
  15. Add Icon to Links
  16. Progress Bar Example

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