Misaligned text/arrows on right side of menu when `userChrome.panel.full_width_padding` = `true`

### Describe the bug

If `userChrome.panel.full_width_padding` is set to `true` in `about:config` or `user.js`, the text/arrows on the right side of menu are misaligned.

### Expected behavior

Menu text/arrows should be aligned when `userChrome.panel.full_width_padding` is set to `true`

### Screenshots


### OS

Windows 11

### OS - Others

_No response_

### Firefox Version

127.0.2 (stable)

### 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
- [ ] 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
user_pref("userChrome.panel.full_width_padding", true);
```

### Additional context

_No response_

Reproduce the menu alignment issue in Firefox on Windows 11 with userChrome.panel.full_width_padding set to true, using the screenshot and issue description as the reference. Inspect the SCSS menu styling and verify that the right-side text and arrows align when the fix is complete.

Written by the indexing model from the issue text.