:default CSS pseudo-class

- UNOFF

The :default pseudo-class matches checkboxes and radio buttons which are checked by default, <option>s with the selected attribute, and the default submit button (if any) of a form.

IE

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

Edge

  1. 12 - 18: Not supported
  2. 79 - 85: Supported
  3. 86: Supported

Firefox

  1. 2 - 3.6: Support unknown
  2. 4 - 80: Supported
  3. 81: Supported
  4. 82 - 83: Supported

Chrome

  1. 4 - 14: Support unknown
  2. 15 - 50: Partial support
  3. 51 - 85: Supported
  4. 86: Supported
  5. 87 - 89: Supported

Safari

  1. 3.1 - 5: Support unknown
  2. 5.1 - 10: Partial support
  3. 10.1 - 13.1: Supported
  4. 14: Supported
  5. TP: Supported

Opera

  1. 9 - 11.5: Support unknown
  2. 11.6 - 12.1: Partial support
  3. 15 - 37: Partial support
  4. 38 - 70: Supported
  5. 71: Supported

iOS Safari

  1. 3.2 - 6.1: Support unknown
  2. 7 - 10.2: Partial support
  3. 10.3 - 13.7: Supported
  4. 14: Supported

Opera Mini

  1. all: Partial support

Android Browser

  1. 2.1 - 3: Support unknown
  2. 4 - 4.4.4: Partial support
  3. 81: Supported

Blackberry Browser

  1. 7: Support unknown
  2. 10: Partial support

Opera Mobile

  1. 10 - 12: Support unknown
  2. 12.1: Partial support
  3. 59: Supported

Chrome for Android

  1. 85: Supported

Firefox for Android

  1. 79: Supported

IE Mobile

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

UC Browser for Android

  1. 12.12: Partial support

Samsung Internet

  1. 4: Partial support
  2. 5 - 11.2: Supported
  3. 12.0: Supported

QQ Browser

  1. 10.4: Supported

Baidu Browser

  1. 7.12: Not supported

KaiOS Browser

  1. 2.5: Supported

Whether <option selected> matches :default (per the spec) was not tested since <select>s and <option>s are generally not styleable, which makes it hard to formulate a test for this.

Resources:
JS Bin testcase
WebKit bug 156230 - `:default` CSS pseudo-class should match checkboxes+radios with a `checked` attribute
MDN Web Docs - CSS :default
HTML specification for `:default`
MS Edge feature request on UserVoice