[Bug] Compatibility with Zen Browser Sidebar Panel

### Prerequisites

- [X] I [searched for any existing report](https://github.com/darkreader/darkreader/issues?q=is%3Aissue) about this bug to avoid opening a duplicate.
- [X] I can reproduce this bug in a new, unmodified web browser profile with Dark Reader installed as the only extension.
- [X] I understand I need to use the [Broken Website Report template](https://github.com/darkreader/darkreader/issues/new?assignees=&labels=Broken+Website&template=broken-website-report.yml&title=%5BBroken+Website%5D+Replace+with+title) if this bug I am reporting occurs on a single website.

### Bug Description

A couple of days ago, a new browser based on Firefox, Zen Browser, was released. It has a feature called "Zen Sidebar," which is a mini version of a normal browser tab. At first, I thought it was a problem with their browser, but after some research ([see this comment](https://github.com/zen-browser/desktop/issues/645#issuecomment-2309347670)), found out that the problem comes from this extension.

### Website Address

-

### Steps To Reproduce

1. Open any light mode web with Zen Browser
2. Open zen sidebar panel
3. Enable Dark Reader
4. Dark mode only applied to normal browser tab

### Expected Behavior

The Dark Reader extension should be applied to the Zen Browser Sidebar Panel.

### Actual Behavior

The Dark Reader extension have no impact to Zen Browser Sidebar Panel.

### Screenshots


### Operating System

Windows 11

### Web Browser name and version

Zen Browser (x64 en-US) 1.0.0-a.29

### Dark Reader version

4.9.88

### Additional Context

_No response_