CSS Flexible Box Layout Module

Method of positioning elements in horizontal or vertical stacks. Support includes all properties prefixed with flex, as well as display: flex, display: inline-flex, align-content, align-items, align-self, justify-content and order.

Chrome

◐ 4 - 20: Partial support
✅ 21 - 28: Supported
✅ 29 - 134: Supported
✅ 135: Supported
✅ 136 - 138: Supported

Edge

✅ 12 - 134: Supported
✅ 135: Supported

Safari

◐ 3.1 - 6: Partial support
✅ 6.1 - 8: Supported
✅ 9 - 18.3: Supported
✅ 18.4: Supported
✅ 18.5 - TP: Supported

Firefox

◐ 2 - 21: Partial support
◐ 22 - 27: Partial support
✅ 28 - 136: Supported
✅ 137: Supported
✅ 138 - 140: Supported

Opera

❌ 9 - 12: Not supported
✅ 12.1: Supported
✅ 15 - 16: Supported
✅ 17 - 116: Supported
✅ 117: Supported

IE

❌ 5.5 - 9: Not supported
◐ 10: Partial support
◐ 11: Partial support

Chrome for Android

✅ 135: Supported

Safari on iOS

◐ 3.2 - 6.1: Partial support
✅ 7 - 8.4: Supported
✅ 9 - 18.3: Supported
✅ 18.4: Supported
✅ 18.5: Supported

Samsung Internet

✅ 4 - 26: Supported
✅ 27: Supported

Opera Mini

✅ all: Supported

Opera Mobile

❌ 10 - 12: Not supported
✅ 12.1: Supported
✅ 80: Supported

UC Browser for Android

✅ 15.5: Supported

Android Browser

◐ 2.1 - 4.3: Partial support
✅ 4.4 - 4.4.4: Supported
✅ 135: Supported

Firefox for Android

✅ 137: Supported

QQ Browser

✅ 14.9: Supported

Baidu Browser

✅ 13.52: Supported

KaiOS Browser

✅ 2.5: Supported
✅ 3: Supported

Most partial support refers to supporting an older version of the specification or an older syntax.

Resources:: Flexbox CSS generator; A Complete Guide to Flexbox; Tutorial on cross-browser support; 10up Open Sources IE 8 and 9 Support for Flexbox; Flexbugs: Repo for flexbox bugs; Ecligrid - Mobile first flexbox grid system; The Difference Between Width and Flex-Basis; Examples on how to solve common layout problems with flexbox; Flexbox playground and code generator; Article on using the latest spec

Sub-features:: gap property for Flexbox