Mismatching captions buttons background with the Tab bar/captions bar

### Describe the bug

No matter what theme is selected in Firefox, the caption buttons background and buttons glyphs themselves are always out of context of the rest of the Firefox theme.

Could this be resolved in any way ?

Any help will be greatly appreciated.

Thanks.

### Expected behavior

_No response_

### Screenshots

Here's a screesnshot: (pay attention to the area in the enclosed circle in the top right corner)

sercontent.com/26643729/225748823-bc2d148f-97fc-45ff-9171-157fd5bbe00c.PNG)

### OS

Windows 10

### OS - Others

_No response_

### Firefox Version

v111

### Distribution

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

### Theme

- [X] Light
- [X] Dark
- [X] Alpenglow (System: Light)
- [X] Alpenglow (System: Dark)
- [X] 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

_No response_

Start by reproducing the caption and Tab bar appearance in Firefox v111 on Windows 10 across the listed themes, focusing on the top-right button area shown in the screenshots. Trace the SCSS styling responsible for those buttons and verify that their backgrounds and glyphs fit each selected theme without disrupting the bars.

Written by the indexing model from the issue text.