Change background color of all text with a Chrome extension

Question

I just started learning the basics of chrome extensions. Using a "Page Redder" extension, which changes the background color of the entire webpage, as a template I would like to make an extension that changes the background color of all text.

Page Redder from https://developer.chrome.com/extensions/samples: background.js:

// Copyright (c) 2011 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Called when the user clicks on the browser action.
chrome.browserAction.onClicked.addListener(function(tab) {
  // No tabs or host permissions needed!
  console.log('Turning ' + tab.url + ' red!');
  chrome.tabs.executeScript({
    code: 'document.body.style.backgroundColor="red"'
  });
});

manifest.json:

{
  "name": "Page Redder",
  "description": "Make the current page red",
  "version": "2.0",
  "permissions": [
    "activeTab"
  ],
  "background": {
    "scripts": ["background.js"],
    "persistent": false
  },
  "browser_action": {
    "default_title": "Make this page red"
  },
  "manifest_version": 2
}

Can I change the following lines of code to select all text instead?

chrome.tabs.executeScript({
        code: 'document.body.style.backgroundColor="red"'

I tried changing it to:

chrome.tabs.insertCSS("content.css")

with content.css:

input[type='text']
{
  background-color: red;
}

but with no success.