[gnome] way to get up/down scroll steppers to differ in gtk3 ?

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http://ubuntuforums.org – in gtk2 applications such as firefox running on my ubuntu desktop, up and down scrollbar steppers look different (up has rounded top, down has rounded bottom) can gtk3 themes be set up to do something similar, perhaps via css classes that pick out the up stepper widget as opposed to down? thanks for any help (Hardware)