Hi. I did not try the mobile detection yet but I set mine to "is on node-webkit" to show a close button for win/mac/linux but it does not seem to work.
Is on platform node-webkit > Closebutton Set Visible
Else > Closebutton Set Invisible
On Touch > Closebutton: Browser.Close
/Update: It does not work in Node Webkit Preview and in the exported project. :(