: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
  2. 11

Edge

  1. 12 - 18
  2. 79 - 81
  3. 83

Firefox

  1. 2 - 3.6
  2. 4 - 75
  3. 76
  4. 77 - 78

Chrome

  1. 4 - 14
  2. 15 - 50
  3. 51 - 81
  4. 83
  5. 84 - 86

Safari

  1. 3.1 - 5
  2. 5.1 - 10
  3. 10.1 - 13
  4. 13.1
  5. TP

Opera

  1. 9 - 11.5
  2. 11.6 - 12.1
  3. 15 - 37
  4. 38 - 67
  5. 68

iOS Safari

  1. 3.2 - 6.1
  2. 7 - 10.2
  3. 10.3 - 13.3
  4. 13.4

Opera Mini

  1. all

Android Browser

  1. 2.1 - 3
  2. 4 - 4.4.4
  3. 81

Blackberry Browser

  1. 7
  2. 10

Opera Mobile

  1. 10 - 12
  2. 12.1
  3. 46

Chrome for Android

  1. 81

Firefox for Android

  1. 68

IE Mobile

  1. 10
  2. 11

UC Browser for Android

  1. 12.12

Samsung Internet

  1. 4
  2. 5 - 10.1
  3. 11.1

QQ Browser

  1. 10.4

Baidu Browser

  1. 7.12

KaiOS Browser

  1. 2.5

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