This is powered by the list of CSS property and values [here](https://github.com/adobe/brackets/blob/master/src/extensions/default/CSSCodeHints/CSSProperties.json).
You can update the prebuilt list of completions by running `node update.js` at the root of this package and checking for changes within `completions.json`. This does rely on having dev dependencies installed, so ensure you install all dependencies before doing so.