How Can I Use CSS Variables in IE11?

IE11 Polyfills for CSS Variables

IE11 lacks support for CSS variables, which presents challenges for mixed-browser web development environments. Fortunately, a solution exists in the form of polyfills or scripts.

CSS Vars Ponyfill

One such polyfill is CSS Vars Ponyfill, available on GitHub and NPM. This lightweight (6kB min gzip), dependency-free library offers various features:

• Client-side transformation of CSS custom properties
• Live updates for runtime values
• Support for chained and nested var() functions
• Compatibility with web components and shadow DOM CSS

Limitations and Considerations

While CSS Vars Ponyfill provides substantial support, it has limitations:

• Custom property support is restricted to :root and :host declarations.
• var() usage is confined to property values, as per W3C specifications.

Example Implementations

The polyfill demonstrates its capabilities with examples such as:

• Root-level custom properties:

  :root {
    --a: red;
  }
  
  p {
    color: var(--a);
  }

• Chained and nested custom properties:

  :root {
    --a: var(--b);
    --b: var(--c);
    --c: red;
  }
  
  p {
    color: var(--a);
  }

• Fallback values:

  p {
    font-size: var(--a, 1rem);
    color: var(--b, var(--c, var(--d, red))); 
  }

• Transformations for CSS imports and web components:

  <link rel="stylesheet" href="/absolute/path/to/style.css">
  <link rel="stylesheet" href="../relative/path/to/style.css">
  
  <style>
    @import "/absolute/path/to/style.css";
    @import "../relative/path/to/style.css";
  </style>

Conclusion

By employing CSS Vars Ponyfill, developers can leverage the benefits of CSS variables even in IE11. This polyfill enables the creation of consistent and reusable styles across modern and legacy browsers, enhancing the flexibility and performance of web applications.

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