Now in Safari TP (42+) and coming with Firefox 58+:
Edge once again the last one missing.
In development in Chrome and Firefox.
Enabled by default in Chrome 60: https://www.chromestatus.com/feature/5363834508279808
Edge is the last one missing: https://caniuse.com/#feat=css-focus-within
Probably obsolete, as you are already developing it: https://developer.microsoft.com/en-us/microsoft-edge/platform/status/webkittextstroke/