Can I use
?

PNG alpha transparency

- REC

Semi-transparent areas in PNG files

Chrome

  1. ✅ 4 - 156: Supported
  2. ✅ 157: Supported
  3. ✅ 158 - 160: Supported

Edge

  1. ✅ 12 - 155: Supported
  2. ✅ 156: Supported

Safari

  1. ✅ 3.1 - 27.1: Supported
  2. ✅ 27.2: Supported
  3. ✅ 27.3 - TP: Supported

Firefox

  1. ✅ 2 - 158: Supported
  2. ✅ 159: Supported
  3. ✅ 160 - 162: Supported

Opera

  1. ✅ 9 - 138: Supported
  2. ✅ 139: Supported

IE

  1. ❌ 5.5: Not supported
  2. ❌ 6: Not supported (but has polyfill available)
  3. ✅ 7 - 10: Supported
  4. ✅ 11: Supported

Chrome for Android

  1. ✅ 157: Supported

Safari on iOS

  1. ✅ 3.2 - 26.6: Supported
  2. ✅ 27.0: Supported
  3. ✅ 27.1 - 27.2: Supported

Samsung Internet

  1. ✅ 4 - 30: Supported
  2. ✅ 31: Supported

Opera Mini

  1. ✅ all: Supported

Opera Mobile

  1. ✅ 10 - 12.1: Supported
  2. ✅ 80: Supported

UC Browser for Android

  1. ✅ 15.5: Supported

Android Browser

  1. ✅ 2.1 - 4.4.4: Supported
  2. ✅ 157: Supported

Firefox for Android

  1. ✅ 159: Supported

QQ Browser

  1. ✅ 14.9: Supported

Baidu Browser

  1. ✅ 13.52: Supported

KaiOS Browser

  1. ✅ 2.5: Supported
  2. ✅ 3: Supported

IE6 does support full transparency in 8-bit PNGs, which can sometimes be an alternative to 24-bit PNGs.

Resources:
Wikipedia