Can I use
?

:placeholder-shown CSS pseudo-class

- WD

Input elements can sometimes show placeholder text as a hint to the user on what to type in. See, for example, the placeholder attribute in HTML5. The :placeholder-shown pseudo-class matches an input element that is showing such placeholder text.

Chrome

  1. 4 - 46: Not supported
  2. 47 - 116: Supported
  3. 117: Supported
  4. 118 - 120: Supported

Edge

  1. 12 - 18: Not supported
  2. 79 - 116: Supported
  3. 117: Supported

Safari

  1. 3.1 - 8: Not supported
  2. 9 - 16.5: Supported
  3. 16.6: Supported
  4. 17.0 - TP: Supported

Firefox

  1. 2 - 3.6: Not supported
  2. 4 - 50: Partial support
  3. 51 - 116: Supported
  4. 117: Supported
  5. 118 - 120: Supported

Opera

  1. 9 - 33: Not supported
  2. 34 - 101: Supported
  3. 102: Supported

IE

  1. 5.5 - 9: Not supported
  2. 10: Partial support
  3. 11: Partial support

Chrome for Android

  1. 117: Supported

Safari on iOS

  1. 3.2 - 8.4: Not supported
  2. 9 - 16.6: Supported
  3. 17.0: Supported
  4. 17.1: Supported

Samsung Internet

  1. 4: Not supported
  2. 5 - 21: Supported
  3. 22: Supported

Opera Mini

  1. all: Not supported

Opera Mobile

  1. 10 - 12.1: Not supported
  2. 73: Supported

UC Browser for Android

  1. 15.5: Supported

Android Browser

  1. 2.1 - 4.4.4: Not supported
  2. 117: Supported

Firefox for Android

  1. 117: Supported

QQ Browser

  1. 13.1: Supported

Baidu Browser

  1. 13.18: Supported

KaiOS Browser

  1. 2.5: Partial support
  2. 3: Supported

For support of styling the actual placeholder text itself, see CSS ::placeholder

Resources:
Firefox bug
WebKit commit