Can I use
?

CSS Variables (Custom Properties)

- CR

Permits the declaration and usage of cascading variables in stylesheets.

IE

  1. 5.5 - 10: Not supported
  2. 11: Not supported

Edge

  1. 12 - 14: Not supported
  2. 15: Partial support
  3. 16 - 93: Supported
  4. 94: Supported

Firefox

  1. 2 - 30: Not supported
  2. 31 - 92: Supported
  3. 93: Supported
  4. 94 - 95: Supported

Chrome

  1. 4 - 47: Not supported
  2. 48: Disabled by default
  3. 49 - 94: Supported
  4. 95: Supported
  5. 96 - 98: Supported

Safari

  1. 3.1 - 9: Not supported
  2. 9.1: Partial support
  3. 10 - 14.1: Supported
  4. 15: Supported
  5. TP: Supported

Opera

  1. 9 - 34: Not supported
  2. 35: Disabled by default
  3. 36 - 79: Supported
  4. 80: Supported

Safari on iOS

  1. 3.2 - 9.2: Not supported
  2. 9.3: Partial support
  3. 10 - 14.8: Supported
  4. 15: Supported

Opera Mini

  1. all: Not supported

Android Browser

  1. 2.1 - 4.4.4: Not supported
  2. 94: Supported

Opera Mobile

  1. 10 - 12.1: Not supported
  2. 64: Supported

Chrome for Android

  1. 94: Supported

Firefox for Android

  1. 92: Supported

UC Browser for Android

  1. 12.12: Supported

Samsung Internet

  1. 4: Not supported
  2. 5 - 14.0: Supported
  3. 15.0: Supported

QQ Browser

  1. 10.4: Not supported

Baidu Browser

  1. 7.12: Not supported

KaiOS Browser

  1. 2.5: Supported
Resources:
Edge Dev Blog post
MDN Web Docs - Using CSS variables
Polyfill for IE11
Mozilla hacks article (older syntax)