This is my Karabiner-Elements configuration.
If you haven't already, download and install Karabiner-Elements.
https://karabiner-elements.pqrs.org/
Be sure and allow Karabiner-Elements in your system preferences.
System Preferences » Security & Privacy » Accessibility
To enable this config, download this repo to ~/.config/karabiner/.
git clone https://github.com/ezrafree/karabiner-config.git ~/.config/karabiner/