blue border around active tab

### Describe the bug

In the latest release there is a blue border around active tab.

### Expected behavior

No blue border 😅

### Screenshots

### OS

Windows 11

### OS - Others

_No response_

### Firefox Version

146.0.1

### 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

- [ ] 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

I always delete the chrome folder and user.js file when upgrading lepton, and also always clean the initialization cache using the button in about:support, I also do not edit the user.js file, it's used stock.

No source file or test is named in the issue. Reproduce the active-tab appearance on Windows 11 with Firefox 146.0.1, the Original Lepton distribution, and the dark theme, then trace the active-tab styling in the SCSS sources. Done means the active tab no longer shows the blue border without changing the reported setup.

Written by the indexing model from the issue text.