---
title: 'Breaking Change: CSS Variable Syntax'
introduction: >
  Older versions of LibSass and Ruby Sass parsed custom property declarations
  just like any other property declaration, allowing the full range of
  [SassScript expressions](/documentation/syntax/structure#expressions) as
  values. But this wasn't compatible with CSS.
---

{% compatibility 'dart: true', 'libsass: "3.5.0"', 'ruby: "3.5.0"' %}{% endcompatibility %}

{% markdown %}
  The CSS spec allows almost any string of characters to be used in a custom
  property declaration. Even though these values might not be meaningful for any
  CSS property, they could be accessed from JavaScript. When they were parsed as
  SassScript values, syntax that would have been valid plain CSS failed to
  parse. For example, the [Polymer library][] used this to support plain-CSS
  mixins:

  [Polymer library]: https://polymer-library.polymer-project.org/3.0/docs/devguide/custom-css-properties#use-custom-css-mixins
{% endmarkdown %}

{% codeExample 'css-vars', false, 'scss' %}
  :root {
    --flex-theme: {
      border: 1px solid var(--theme-dark-blue);
      font-family: var(--theme-font-family);
      padding: var(--theme-wide-padding);
      background-color: var(--theme-light-blue);
    };
  }
  ===
  :root {
    --flex-theme: {
      border: 1px solid var(--theme-dark-blue);
      font-family: var(--theme-font-family);
      padding: var(--theme-wide-padding);
      background-color: var(--theme-light-blue);
    };
  }
{% endcodeExample %}

{% markdown %}
  To provide maximum compatibility with plain CSS, more recent versions of Sass
  require SassScript expressions in custom property values to be written within
  [interpolation](/documentation/interpolation). Interpolation will also work
  for older Sass versions, and so is recommended for all stylesheets.
{% endmarkdown %}

{% codeExample 'css-vars-interpolation' %}
  $accent-color: #fbbc04;

  :root {
    // WRONG, will not work in recent Sass versions.
    --accent-color-wrong: $accent-color;

    // RIGHT, will work in all Sass versions.
    --accent-color-right: #{$accent-color};
  }
  ===
  $accent-color: #fbbc04

  :root
    // WRONG, will not work in recent Sass versions.
    --accent-color-wrong: $accent-color

    // RIGHT, will work in all Sass versions.
    --accent-color-right: #{$accent-color}
  ===
  :root {
    --accent-color-wrong: $accent-color;
    --accent-color-right: #fbbc04;
  }
{% endcodeExample %}

{% headsUp false %}
  {% markdown %}
    Because interpolation removes quotation marks from quoted strings, it may be
    necessary to wrap them in the [`meta.inspect()` function][] to preserve
    their quotes.

    [`meta.inspect()` function]: /documentation/modules/meta#inspect
  {% endmarkdown %}

  {% codeExample 'css-vars-heads-up' %}
    @use "sass:meta";

    $font-family-monospace: Menlo, Consolas, "Courier New", monospace;

    :root {
      --font-family-monospace: #{meta.inspect($font-family-monospace)};
    }
    ===
    @use "sass:meta"

    $font-family-monospace: Menlo, Consolas, "Courier New", monospace

    :root
      --font-family-monospace: #{meta.inspect($font-family-monospace)}
    ===
    :root {
      --font-family-monospace: Menlo, Consolas, "Courier New", monospace;
    }
  {% endcodeExample %}
{% endheadsUp %}