browser.action.onClicked.addListener((tab) => {
  // Inject the CSS for the hover highlight
  browser.scripting.insertCSS({
    target: { tabId: tab.id },
    files: ["content.css"]
  });

  // Inject the JavaScript for the element picker
  browser.scripting.executeScript({
    target: { tabId: tab.id },
    files: ["content.js"]
  });
});