CSS Generated content for pseudo-elements

- REC

Method of displaying text or images before or after the given element's contents using the ::before and ::after pseudo-elements. All browsers with support also support the attr() notation in the content property.

IE

  1. 5.5 - 7: Not supported
  2. 8: Partial support
  3. 9 - 10: Supported
  4. 11: Supported

Edge

  1. 12 - 91: Supported
  2. 92: Supported

Firefox

  1. 2 - 89: Supported
  2. 90: Supported
  3. 91 - 92: Supported

Chrome

  1. 4 - 91: Supported
  2. 92: Supported
  3. 93 - 95: Supported

Safari

  1. 3.1 - 14: Supported
  2. 14.1: Supported
  3. 15 - TP: Supported

Opera

  1. 9 - 76: Supported
  2. 77: Supported

Safari on iOS

  1. 3.2 - 14.4: Supported
  2. 14.5: Supported

Opera Mini

  1. all: Supported

Android Browser

  1. 2.1 - 4.4.4: Supported
  2. 92: Supported

Opera Mobile

  1. 10 - 12.1: Supported
  2. 64: Supported

Chrome for Android

  1. 92: Supported

Firefox for Android

  1. 90: Supported

UC Browser for Android

  1. 12.12: Supported

Samsung Internet

  1. 4 - 13.0: Supported
  2. 14.0: Supported

QQ Browser

  1. 10.4: Supported

Baidu Browser

  1. 7.12: Supported

KaiOS Browser

  1. 2.5: Supported

For content to appear in pseudo-elements, the content property must be set (but may be an empty string).

Resources:
Guide on usage
Dev.Opera article
WebPlatform Docs