Hi Brian!
To create buttons, as you want, you should set Properties for Buttons:
Inline: checked
Icon: None
Text: Keep empty
push More Properties - add "padding" with value=0
Next changes will not visible in Appery Editor, but they will be in preview and application:
Add event "Load" on page with buttons, and set Action "Run JavaScript"
add next JavaScript:
pre
Appery("mobilebutton_1").css("background-image", 'url(' + Appery.getImagePath('logo') + ".jpg" + ')');
/pre
where "mobilebutton_1" - name of your button
"logo" - name of image asset
"jpg" - extension of image asset.