Make navigation menu always visible when scrolling the content of the settings

### Please answer the following questions for yourself before submitting an issue

- [x] Filters were updated before reproducing an issue
- [x] I checked the [knowledge base](https://adguard.com/kb/) and found no answer
- [x] I checked to make sure that this issue has not already been filed

### AdGuard Extension version

5.1.79

### Browser version

Chrome 136

### OS version

macOS 15.4.1

### Ad Blocking

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### Privacy

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### Social

_No response_

### Annoyances

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### Security

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### Other

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### Language-specific

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### Issue Details

Steps to reproduce:
1. Open `chrome-extension://gfggjaccafhcbfogfkogggoepomehbjl/pages/options.html#/stealth`
2. Scroll to the end of the page

### Expected Behavior

The navigation menu remains fully visible when scrolling.

### Actual Behavior

The navigation menu scrolls with the main content.

### Screenshots

Screenshot 1


### Additional Information

The same problem with MV3 extension.

You need to add `poistion: fixed;` to `.sidebar`.