userChrome.theme.transparent.panel option made chat and other panels complete see through

### Describe the bug

Chat panel(and others) is without a background after option enable.

### Expected behavior

It should be semi-transparent.

### Screenshots


### OS

Windows 10

### OS - Others

_No response_

### Firefox Version

138.1

### Distribution

- [ ] [Original Lepton](https://github.com/black7375/Firefox-UI-Fix)
- [ ] [Lepton's photon style](https://github.com/black7375/Firefox-UI-Fix/tree/photon-style)
- [x] [Lepton's proton style](https://github.com/black7375/Firefox-UI-Fix/tree/proton-style)

### Theme

- [ ] Light
- [x] Dark
- [ ] Alpenglow (System: Light)
- [ ] Alpenglow (System: Dark)
- [ ] System Default
- [ ] Others: (e.g. [Photon Colors](https://addons.mozilla.org/en-US/firefox/addon/photon-colors/), [Google Chrome Dark](https://addons.mozilla.org/en-US/firefox/addon/google-chrome-dark/), [Fairytale Of Nature](https://addons.mozilla.org/en-US/firefox/addon/fairytale-of-nature/))

### Theme - More Info

_No response_

### `user.js` setup

user.js setup

```javascript
// Your settings
```

### Additional context

Its appears that reason for this is panel background have been set to complete transparent and background for panel view is set to semi-transparent in order to make it semi-transparent.

Reverse the process should fix this.

Start by inspecting the proton-style SCSS rules for panel backgrounds and the userChrome.theme.transparent.panel option. Reproduce the issue with the reported Windows 10, Firefox 138.1, dark-theme setup, then verify that chat and other panels retain the expected semi-transparent background without affecting the intended transparency.

Written by the indexing model from the issue text.