gtk css help: removing gaps between tabs

[sbirch-fl]

After finally upgrading to Ghostty 1.2.something, I'm just trying to make Ghostty's badwaita tabs look tolerable in KDE Plasma with the Breeze Light theme. Spent several hours just trying to remove the gaps between the tabs. Now I just want someone to fix it for me or I'll cry. Here's what I have so far:

tabbar tabbox {
  margin: 0;
  padding: 0;
  min-height: 10px;
}

tabbar tabbox tabboxchild {
  border-radius: 0;
  border-left: #c6c8c9 solid 1px;
  border-right: #c6c8c9 solid 1px;
}

tabbar tabbox tab {
  margin: 0;
  padding: 0;
  border-radius: 0;
  border-top: transparent solid 3px;
  background-color: #c7c8c9;
}

tabbar tabbox tab:selected {
  border-top: #3daee9 solid 3px;
  background-color: #eff0f1;
}

tabbar tabbox tab label {
  font-size: 13px;
}

(Yes, I know that border-top: transparent solid 3px in inactive tabs is the wrong way to make the tab labels line up.)

Anyone successfully made the tabs cuddle right up next to each other like they do in Qt apps? Thanks.

P.S., if the idea is for the Gtk app to defer to libadwaita for widget look & feel, with only gtk "css" injection as an escape hatch, then oh boy would I be thrilled for a Qt app to exist at some point, because I've had it up to here with all things Gtk today.