Next, we'll go back into the Main Administration menu and visit the Appearance page:

This link takes to an administrative page where you can browse all themes and instantly switch your site into any of those available.

When you visit the page, you'll note that the currently active (default theme) is Bartik.

The other currently enabled theme is Seven and that is in use as the current administration theme and when create and editing content.

If you scroll down to the bottom of the page, you will also see an area labeled Uninstalled themes which currently only contains Stark.

The Stark theme is designed to show you what the raw Drupal HTML markup will look like without any kind of style applied.

Try clicking on the Install and set as default link to see it in action:

Having set Stark as the default, you'll need to click on the Back to site link in Toolbar to see it in action because the screen that you are currently on is an administrative page and is therefore using the Seven theme.

Having...