# jhildenbiddle/css-vars-ponyfill

Client-side support for CSS custom properties (aka "CSS variables") in legacy and modern browsers

Repository: https://github.com/jhildenbiddle/css-vars-ponyfill
Canonical: https://ross.abutalabs.com/products/css-vars-ponyfill
Homepage: https://jhildenbiddle.github.io/css-vars-ponyfill
Language: JavaScript
License: MIT
License Family: permissive
Topics: client, client-side, css, custom-properties, custom-property, ie, ie9, ie10, ie11, internet-explorer, javascript, legacy, module, polyfill, ponyfill, shadow, shadow-dom, variables, vars, web-component
Last push: 2024-03-05T21:36:28+00:00

## Health v2 (maintenance only)
Score: 32/100 (v2, computed 2026-09-03T02:20:16.233290+00:00)
- activity 0, release rhythm 35, longevity 100
- inputs: {"age_days": 3208, "days_push": 911, "days_rel": null, "gap_med": null, "n_releases_24m": 0}
- flags: no_releases
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 1460, forks 63 (observed 2026-08-28T04:04:47.380552+00:00)

## What it is
A lightweight, dependency-free JavaScript ponyfill that provides client-side support for CSS custom properties (CSS variables) in legacy and modern browsers. It transforms CSS custom properties into static values at runtime, supporting link/style/import stylesheets, chained and nested var() functions, fallback values, and web components with shadow DOM.

## Use cases
- support CSS variables in Internet Explorer 9-11
- make CSS custom properties work in legacy browsers
- runtime theming with CSS variables across old and new browsers
- use CSS variables inside web components and shadow DOM
- live-update CSS variable values without page reload
- transform stylesheets to static values client-side

## When to choose
- you must support legacy browsers like IE9-IE11 that lack CSS custom property support
- you need runtime/live updates of CSS variable values in older browsers
- your project uses web components or shadow DOM with CSS variables
- you want a small, dependency-free client-side solution

## When to avoid
- your target browsers natively support CSS custom properties
- you modify styles via CSSOM APIs, which this library does not support
- you need custom property declarations outside :root and :host rulesets
- you need a true polyfill that patches the CSSOM rather than transforming stylesheets

## Facets
- artifact type: library
- maturity: maintenance
- function: ui-components, developer-tools
- domain: web-development, frontend, cross-platform
- platform: browser
- tags: css-variables, ponyfill, polyfill, legacy-browser-support, internet-explorer, shadow-dom, web-components, client-side, web-server

## Member repositories
- jhildenbiddle/css-vars-ponyfill (main) score 32

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:04:47.380552+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-30T04:35:24.655032+00:00, confidence not recorded.
  - readme: https://github.com/jhildenbiddle/css-vars-ponyfill (fetched 2026-08-28T04:04:47.380552+00:00, sha f1baff1effad)
  - homepage: https://jhildenbiddle.github.io/css-vars-ponyfill (fetched 2026-08-29T11:44:28.205660+00:00, sha 2b5000526110)
  - registry_npm: https://registry.npmjs.org/css-vars-ponyfill (fetched 2026-08-29T11:44:28.208358+00:00, sha cc6546cec7f0)
- Data as of 2026-08-30T08:39:29.467469+00:00.