[Error] Themes don't integrate (openSUSE Tumbleweed host/guest)

Neither Qt nor GTK themes installed on an openSUSE Tumbleweed host are available within a Tumbleweed container.

**To Reproduce**
1. `distrobox ephemeral`
2. Observe `Integrating host's themes, icons, fonts... [ OK ]`
3. Launch any GTK or Qt graphical application from inside the box (I tested Geany and KWrite)

**Expected behavior**
It looks good.

**Logs**
Unavailable, pending #757.

**Desktop (please complete the following information):**
- Are you using podman or docker?
- Which version or podman or docker?
- Which version of distrobox?