Introspection via JS/CSS to determine if a page currently resides within a Web Panel

[Anomalocaris]

Using JavaScript and/or CSS media queries, is it possible for a webpage to determine - with complete or high certainty - if it currently resides within a Vivaldi Web Panel?

Usage scenario: I would like to have specific bits of user CSS apply to several websites and my OpenWRT router's web-based interface only when they're inside a Web Panel. I know I can achieve this e.g. using a CSS media query like @media only (min-width: foo) and (max-width: bar), but this would also be applied in situations such as when the page is open in a regular tab and I've resized the browser window itself to fall within the rule's scope.

Cheers.

[oudstand]

@Anomalocaris I did something like this in a different mod:

setTimeout(function waitDialog() {
    const browser = document.getElementById('browser');
    if (!browser) {
        setTimeout(waitDialog, 300);
        return;
    }
    chrome.webNavigation.onCompleted.addListener((details) => {
        let fromPanel = false,
            webview = document.querySelector(`.webpanel-content webview[src*="${details.url}"]`);
        
            if (webview) fromPanel = true;
            else webview = document.querySelector(`webview[tab_id="${details.tabId}"]`);

        webview?.executeScript({code: `(${setUrlClickObserver})(${fromPanel})`});
    });
}