Configure them from the GalliumOS/Whisker Menu, in Settings >> Keyboard >> Layout >> Keyboard Model. You access media and function keys either with or without pressing the selected “Overlay” key first ...
GalliumOS is a Chromebook-specific Linux variant. It lets you put a real Linux distro on a Chromebook. My recent review of a new Chromebook feature — the ability to run Linux apps on some Chromebook ...