Drupal themes are a collection of files that determine the visual styling for a website. Themes usually contain several PHP, CSS, and image files, and include the arrangement of blocks in various regions, different layouts on different pages, and the selection of colors, fonts, and graphics.
By default, Drupal 7 includes several themes that you can use or modify, including Bartik, Garland, Seven, and Stark. You can also download a contributed theme from drupal.org, or create your own theme from an existing theme or from scratch.
Drupal modules can also define functions that can be addressed by your website's theme.
To view your installed themes or to select a different theme to use with your website, in the Drupal 7 admin menu, click Appearance.
Finding a contributed theme
For a list of available themes that have been created to address many particular needs, see Download & Extend on drupal.org.
Viewing additional information
For more information about how to work with themes to change how your website is displayed to website visitors, see the Theming Guide on drupal.org.