[Bug] Theme: Adapt to System does not work in XFCE

### Bug Description

I am unsure how the feature "adapt to system" for theming works, but in XFCE does nothing regardless what theme is being selected. What is the app looking for?

### How to Reproduce

Change the theme to "adapt to the system" in XFCE.

### Expected Behavior

Sync with the system's theme. Either use the system's theme or use dark/light variations of the app's theme.

### Operating System

Arch Linux with XFCE - kernel 6.1

### AppFlowy Version(s)

0.3.3

### Screenshots

_No response_

### Additional Context

_No response_