Equals button missing background tint when using latte accent colour

### What Happened?

When using the new Latte accent colour, the background on the equals (`=`) button goes transparent.
- On light mode the `=` symbol is also white, not black like other inputs, making it impossible to read on the white background. The white text only applies when the window is focused. When in the background, the symbol is grey like the rest of the UI.

- On dark mode the button is readable, but still no accent tint.

### Steps to Reproduce

1. Set accent colour to Latte
2. Set apparence to light mode (for impossible to read button) or dark mode (missing accent tint)
3. Focus the calculator window

### Expected Behavior

Button uses latte colour tint like like other accent colours.
On light mode, `=` symbol is black like other inputs when the window is focused

### OS Version

8.x (Circe)

### OS Architecture

amd64 (on most hardwares)

### Session Type

Secure Session (Wayland, This is the default)

### Software Version

Latest release (I have run all updates)

### Log Output

```shell

```

### Hardware Info

_No response_