In 'Yaru-dark' theme, active tab's title is not readable

**Describe the bug**

On Ubuntu 20.04, using Guake installed from apt, when I select 'yaru-dark' theme, the 'title' of the active tab cannot be read.

**Expected behavior**


In other themes, the active tab's name can be read

**Actual behavior**


Notice how the active tab's name cannot be read

**To Reproduce**

- Install guake from apt in Ubuntu 20.04
- Select 'yaru-dark' theme and 'hipster green' color palette (although this also occurred in other palettes that I tested)

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Please run `$ guake --support`, and paste the results here. Don't put backticks (`` ` ``) around it! The output already contains Markdown formatting. And make sure you run the command **OUTSIDE** the Guake.

$ guake --support

Guake Version: 3.6.3

Vte Version: 0.60.3

Vte Runtime Version: 0.60.3

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GTK+ Version: 3.24.20

GDK Backend: GdkX11.X11Display

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Desktop Session: ubuntu

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Display: :0

RGBA visual: True

Composited: True

* Monitor: 0 - LGD DP-2
* Geometry: 1920 x 1080 at 0, 0
* Size: 382 x 215 mm²
* Primary: True
* Refresh rate: 75.00 Hz
* Subpixel layout: unknown