Can I use
?

rem (root em) units

- CR

Type of unit similar to em, but relative only to the root element, not any parent element. Thus compounding does not occur as it does with em units.

IE

  1. 5.5 - 8: Not supported
  2. 9 - 10: Partial support
  3. 11: Supported

Edge

  1. 12 - 85: Supported
  2. 86: Supported

Firefox

  1. 2 - 3.5: Not supported
  2. 3.6 - 80: Supported
  3. 81: Supported
  4. 82 - 83: Supported

Chrome

  1. 4 - 85: Supported
  2. 86: Supported
  3. 87 - 89: Supported

Safari

  1. 3.1 - 4: Not supported
  2. 5 - 13.1: Supported
  3. 14: Supported
  4. TP: Supported

Opera

  1. 9 - 11.5: Not supported
  2. 11.6 - 70: Supported
  3. 71: Supported

iOS Safari

  1. 3.2: Not supported
  2. 4 - 4.3: Supported
  3. 5: Partial support
  4. 6 - 13.7: Supported
  5. 14: Supported

Opera Mini

  1. all: Supported

Android Browser

  1. 2.1 - 4.4.4: Supported
  2. 81: Supported

Blackberry Browser

  1. 7: Supported
  2. 10: Supported

Opera Mobile

  1. 10 - 11.5: Not supported
  2. 12 - 12.1: Supported
  3. 59: Supported

Chrome for Android

  1. 85: Supported

Firefox for Android

  1. 79: Supported

IE Mobile

  1. 10: Supported
  2. 11: Supported

UC Browser for Android

  1. 12.12: Supported

Samsung Internet

  1. 4 - 11.2: Supported
  2. 12.0: Supported

QQ Browser

  1. 10.4: Supported

Baidu Browser

  1. 7.12: Supported

KaiOS Browser

  1. 2.5: Supported
Resources:
Article on usage
REM Polyfill