CSS Flexible Box Layout Module

- CR

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.

IE

  1. 5.5 - 9
  2. 10
  3. 11

Edge

  1. 12 - 83
  2. 84

Firefox

  1. 2 - 21
  2. 22 - 27
  3. 28 - 78
  4. 79
  5. 80 - 81

Chrome

  1. 4 - 20
  2. 21 - 28
  3. 29 - 83
  4. 84
  5. 85 - 87

Safari

  1. 3.1 - 6
  2. 6.1 - 8
  3. 9 - 13
  4. 13.1
  5. 14 - TP

Opera

  1. 9 - 12
  2. 12.1
  3. 15 - 16
  4. 17 - 68
  5. 69

iOS Safari

  1. 3.2 - 6.1
  2. 7 - 8.4
  3. 9 - 13.3
  4. 13.4
  5. 14.0

Opera Mini

  1. all

Android Browser

  1. 2.1 - 4.3
  2. 4.4 - 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. 84

Firefox for Android

  1. 68

IE Mobile

  1. 10
  2. 11

UC Browser for Android

  1. 12.12

Samsung Internet

  1. 4 - 11.2
  2. 12.0

QQ Browser

  1. 10.4

Baidu Browser

  1. 7.12

KaiOS Browser

  1. 2.5

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