display: run-in

- CR

If the run-in box contains a block box, same as block. If a block box follows the run-in box, the run-in box becomes the first inline box of the block box. If an inline box follows, the run-in box becomes a block box.

Chrome

  1. 4 - 31: Supported
  2. 32 - 130: Not supported
  3. 131: Not supported
  4. 132 - 134: Not supported

Edge

  1. 12 - 130: Not supported
  2. 131: Not supported

Safari

  1. 3.1 - 4: Supported
  2. 5 - 6: Supported
  3. 6.1: Support unknown
  4. 7 - 18.0: Not supported
  5. 18.1: Not supported
  6. 18.2 - TP: Not supported

Firefox

  1. 2 - 132: Not supported
  2. 133: Not supported
  3. 134 - 136: Not supported

Opera

  1. 9 - 18: Supported
  2. 19 - 113: Not supported
  3. 114: Not supported

IE

  1. 5.5 - 7: Not supported
  2. 8 - 10: Supported
  3. 11: Supported

Chrome for Android

  1. 131: Not supported

Safari on iOS

  1. 3.2: Supported
  2. 4 - 7.1: Supported
  3. 8 - 18.0: Not supported
  4. 18.1: Not supported
  5. 18.2: Not supported

Samsung Internet

  1. 4 - 25: Not supported
  2. 26: Not supported

Opera Mini

  1. all: Supported

Opera Mobile

  1. 10 - 12.1: Supported
  2. 80: Not supported

UC Browser for Android

  1. 15.5: Not supported

Android Browser

  1. 2.1 - 4.4: Supported
  2. 4.4.3: Not supported
  3. 131: Not supported

Firefox for Android

  1. 132: Not supported

QQ Browser

  1. 14.9: Not supported

Baidu Browser

  1. 13.52: Not supported

KaiOS Browser

  1. 2.5: Not supported
  2. 3: Not supported
Resources:
Mozilla bug report
CSS Tricks article