vertical sizes of taskbar buttons for existing windows are larger than for new windows

[ivomac]

Minimal config:

• Waybar v0.12.0
• No style.css

{
	"position": "left",
	"modules-left": [
		"wlr/taskbar"
	],
	"modules-center": [],
	"modules-right": [],
	"wlr/taskbar": {
		"tooltip": true,
		"icon-size": 16,
		"sort-by-app-id": true,
		"on-click": "activate",
		"on-click-middle": "close"
	}
}

Problem:

1. Start a vertical waybar with taskbar module.
2. Open a few windows: The spacing between the taskbar buttons is normal.
3. Reload waybar: The taskbar button spacing of the existing windows becomes larger.
4. Open a new window: The taskbar button spacing of the new window is normal.

This creates non-uniform spacing between the taskbar buttons when reloading waybar, for example to change the theme config.

The three screenshots show the result of 2. 3. 4. :

[ivomac]

From debug mode I saw that the taskbar gtk widgets have this structure:

box#taskbar.vertical.module:dir(ltr)
  button.flat.active:dir(ltr)
    box.vertical:dir(ltr)
      label:dir(ltr)
      image:dir(ltr)
      label:dir(ltr)
  button.flat:dir(ltr)
    box.vertical:dir(ltr)
      label:dir(ltr)
      image:dir(ltr)
      label:dir(ltr)
...

Adding different background colors to each element, I see something like below. The black boxes above and below the icons are the label elements. They seem to be the cause of the issue.

[ivomac]

I am using this as workaround:

#taskbar button box label {
	all: unset;
	margin: -999px;
}

It removes the label boxes completely so it's fixed for me.