Support DevTools Dark/Light Theme

[warrenbuckley]

Browser Devtools support a dark or light theme, currently the UI is set to dark and doesn't work if I was to change it to a light theme

// Firefox uses onThemeChanged event, Chrome uses setThemeChangeHandler
if (browser.devtools.panels.onThemeChanged) {
    browser.devtools.panels.onThemeChanged.addListener(this._onThemeChanged);
} else {
    // Chrome uses setThemeChangeHandler (Chrome 99+) instead of onThemeChanged
    chrome?.devtools.panels.setThemeChangeHandler(this._onThemeChanged);
}

// Set a data attribute data-theme="dark" on a DOM element 

Firefox (MDN)

https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/devtools/panels/onThemeChanged

Chromium

https://developer.chrome.com/docs/extensions/reference/api/devtools/panels#method-setThemeChangeHandler