Drupal core includes selectable core themes, which customize the aesthetic “look and feel” of the site
Contributed themes adapt or replace a Drupal site’s default look and feel.
Drupal themes use standardized formats that may be generated by common third-party theme design engines. Many themes for Drupal are written in the PHPTemplate engineor, to a lesser extent, the XTemplate engine. Some templates use hard-coded PHP.
Many sites such as Rocket Theme offer free and paid-for themes. Typically paid-for themes still allow extensive customisation and removable of all branding from the creator.