With Chrome Themes you can Personalize your Chromebook browser. Its easy to install Chrome OS themes on your Google Chromebook. First go to Themes Gallery and select your favourite theme there and Click Apply. After this you can see the new theme on your Google Chromebook Browser.
Or you can use the third-party themes in the Chrome Web Store, here is the method to install it.
1. Visit the Web Store at http://chrome.google.com/webstore. You can also reach it by clicking the icon in the “Apps” section of the New Tab page.
2. Browse or search for the theme you’d like to install.
3. On the theme’s details page, click the Install button.
Thats it, you new theme is installed on your Chrome book
How to Reset the theme
You can reset the theme back to the default classic theme.
1. Click the wrench icon on the browser toolbar.
2. Select Settings.
3. Click the Personal Stuff tab.
4. In the “Themes” section, click Reset to default theme.
Read Also: How to Update your Google Chromebook