title: chrome extension changing element color
body: <p>I'm trying to change all <code>h1</code>'s background color to red for example.</p>
  
  <p>At my popup.js that is linked to popup.html I've added this code:</p>
  
  <pre><code>chrome.tabs.executeScript(null,
        {code:"document.getElementsByTagName('h1').style.backgroundColor='red';"});
  </code></pre>
  
  <p>it works fine with <code>document.body</code>, but I have no idea how to make it works with <code>getelementbytagname</code></p>
  
  <p>Also I'd like to add some text in the <code>h1</code> container.</p>