Modifying Chrome's Appearance with Actions and Themes
Before we get into writing any code, let's consider the different ways in which we can modify the browser's functionality. Actions affect one or more web pages. A browser action is a button that lives in the toolbar to the right of the Omnibox and is relevant to most web pages. A page action is only relevant for a few pages. Action icons live inside the Omnibox to the far right. Both types of actions can be composed of an icon, a pop-up, a tool tip, and a badge, but none of these components are required.
Whereas actions modify the content of pages, themes can change how the browser itself looks. Themes allow you to select background images for blank tabs, affect some colors, and control the basic color scheme of the browser window.