Themes allow you to change the look and feel of your Drupal site. You can use themes contributed by others or create your own.
Placing downloaded and custom themes in this directory separates downloaded and custom themes from Drupal core's themes. This allows Drupal core to be updated without overwriting these files.
Contributed themes from the Drupal community may be downloaded at https://www.drupal.org/project/project_theme.
In multisite configurations, themes found in this directory are available to all sites. Alternatively, the sites/your_site_name/themes directory pattern may be used to restrict themes to a specific site instance.
Refer to the "Appearance" section of the README.txt in the Drupal root directory for further information on customizing the appearance of Drupal with custom themes.