I am building my first SharePoint hosted add-in and have added a CustomAction to document libraries.
The command works, but has a default icon (orange dot).
I have tried to change the value of the Image16by16 attribute of the Button element in the Elements.xml file, but so far without succes. Everything else than the default '_layouts/15/images/placeholder16x16.png' results in no icon at all.
I have tried referencing an image in the app web (~appWebUrl/..., which I would prefer), or an image in the Site Assets of the host web.
Should this be possible at all, and if so, what is the syntax to refer to either app web or host web in this attribute?
If it is not possible, is there a list of available images in _layouts/15/images?
