So the spinner.increment does work on the popup too, but you have to have a value in it (value is not empty but is zero)
For styling you can change the theme.css (or use injection)
for the buttons
.ia_numericEntryFieldComponent__modal_content > .ia_numericEntryFieldComponent__modal_buttons > button {}
for the pencils (note its an svg)
.ia_numericEntryFieldComponent__editIcon{}
and
.ia_numericEntryFieldComponent__editIcon--active{}