indeterminate checkbox

- LS

Indeterminate checkboxes are displayed in a state which is distinct both from being checked or being unchecked. They are commonly used in hierarchical checkboxes to indicate that only some of the checkbox's descendants are checked.

IE

  1. 5.5: Support unknown
  2. 6 - 10: Supported
  3. 11: Supported

Edge

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

Firefox

  1. 2 - 3: Not supported
  2. 3.5: Support unknown
  3. 3.6 - 80: Supported
  4. 81: Supported
  5. 82 - 83: Supported

Chrome

  1. 4 - 27: Not supported
  2. 28 - 85: Supported
  3. 86: Supported
  4. 87 - 89: Supported

Safari

  1. 3.1 - 5.1: Not supported
  2. 6 - 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 - 12.1: Not supported
  2. 12.2 - 13.7: Supported
  3. 14: Supported

Opera Mini

  1. all: Not supported

Android Browser

  1. 2.1 - 4.3: Not supported
  2. 4.4 - 4.4.4: Supported
  3. 81: Supported

Blackberry Browser

  1. 7: Not supported
  2. 10: Not supported

Opera Mobile

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

Indeterminacy does not affect a checkbox's checkedness state. It merely affects how the checkbox is displayed.

Resources:
iOS versions below 12 don't support indeterminate checkboxes (WebKit Bug 160484)
CSS-Tricks article