It's the entire window. But you can work around this, here's the old click-to-cure code from ProfitUI 3.x, was pretty groundbreaking at the time because it was the first to avoid targeting your pet:
<Button MouseOverTextColor="#FF0000" Name="CureEffect1" NormalTextColor="#FFFFFF" OnHoverIn="target_allow_pet_self_toggle 0" OnHoverOut="target_allow_pet_self_toggle 1" OnPress="useability Cure Trauma
target_previous" Opacity="0.000" Size="18,18" Style="/Profit.invisible" Tooltip="Cure Trauma" />
If you want to include potion curing look at the ProfitUI 4.x code, that has become a bit complicated though and is spread across several files, so I thought it's easier to quote the old code.