How to access the source code of an open tab?

Question

JavaScript

Hi. I am writing an extension for chrome. In the open tab, I click on the extension, it should change the background of the site. But nothing happens, the console is clean.

chrome.browserAction.onUpdated.addListener(function(tab) {
    chrome.tabs.executeScript(tab.id,{code:"document.body.style.background='red'"});
});