A simple way to toggle between dark and light themes in Sublime Text 3.
Copy the code in Default (OSX).sublime-keymap
to your keybindings (Preferences > Key Bindings - User)
Change the keybinding, color schemes, themes, and fonts to your preferences
Copy the file ToggleColorSchemeCommand.py
to ~/Library/Application Support/Sublime Text 3/Packages/User/
Toggle with alt+down.