title: Chrome Extension PopUp Button not Functioning
body: <p>I'm currently creating a chrome extension for dyslexia and am trying to link a button press in the popup for the extension to changing the font size of the page as an initial step, but I'm having trouble making it work. The issue is that nothing happens upon pressing the button in the pop up.  </p>
  
  <p>Here is the html for the pop up: </p>
  
  <pre><code>&lt;!DOCTYPE html&gt;
    &lt;html&gt;
      &lt;head&gt;
        &lt;style&gt;
          button {
            height: 30px;
            width: 30px;
            outline: none;
          }
        &lt;/style&gt;
      &lt;/head&gt;
      &lt;body&gt;
  &lt;button id="changeFont"&gt;&lt;/button&gt;
   &lt;script src="popup.js"&gt;&lt;/script&gt;
      &lt;/body&gt;
    &lt;/html&gt;
  </code></pre>
  
  <p>Here is the source file for the popup html: </p>
  
  <pre><code> let changeFont = document.getElementById('changeFont');
  changeFont.onclick = function(element) {
      chrome.tabs.executeScript({
      code:
      'var elements = document.getElementsByTagName('*');'+ 
      'for (var i = 0; i &lt; elements.length; i++) {'   +
      'var element = elements[i];' +
          'element.style.fontSize = "50px";'+
          '}'
                   });
        };
  </code></pre>
  
  <p>Last, here is the manifest file: </p>
  
  <pre><code>{
  "manifest_version": 2,
      "name": "Dyslexipro",
      "description": "dyslexia aid ",
      "version": "1.0",
      "permissions": ["activeTab",
          "tabs","declarativeContent","storage"],
      "browser_action": {
      "default_popup": "popup.html",
      "default_icon": {
          "16": "images/get_started16.png",
          "32": "images/get_started32.png",
          "48": "images/get_started48.png",
          "128": "images/get_started128.png"
        }
  
      },
      "icons": {
        "16": "images/get_started16.png",
        "32": "images/get_started32.png",
        "48": "images/get_started48.png",
        "128": "images/get_started128.png"
      },
     "background": {
         "scripts": ["content.js","popup.js"],
        "persistent": true
      }
  }
  </code></pre>