Less padding inside/between taskbar items?

To use my screen space more optimally, I'd like a way to decrease all the extra spacing and padding which Basic/Aero themes insert inside and around items on the taskbar. The default Classic theme has much less padding there - that's what I want to have in Aero and Basic.

These are the elements I'm talking about:
- The spacing between toolbar icons (like the Quicklaunch toolbar which I've re-enabled)
- The padding *inside* taskbar buttons
- The spacing between notification area (system tray) icons

So far, the only way I've found to make the taskbar more compact was to decrease the size of 'Caption Buttons' (under "advanced appearance settings")... but this shrinks down all graphical elements, including icons - not just the caption buttons. I want to keep them at the default size (16x16?), just with less padding.

I've seen custom themes that do this, so I know the setting can be changed - how do I control this myself (while using an arbitrary theme)? I've never used a theme customizer or similar, so a detailed answer would be appreciated.

thanks!

Thanks, but nope that's not it... I've already tried all the easily-accessible settings like these- they do let you modify the icon sizes (I'm already using small icons), but not the padding between them or the spacing around them.

I guess that's an internal theme setting and I'd need some theme editor/style builder to change it??