Working with Base and Subthemes
Chances are you have a certain way you do things. You may tend to structure your markup similarly in all your themes. You might frequently override certain theme functions, or have special way you like to style forms, or maybe you tend to use a certain grid framework for your layout. These are all great reasons to take advantage of Drupal’s base and subtheming functionality.
Subthemes share a special relationship with their base (parent) theme(s). They inherit template files and assets from their parent themes. This makes them a great tool to help streamline your theming workflow and essentially create your own “frameworks” or “resets” for theming Drupal sites. Of course, you can also use an existing base theme. Drupal offers quite a few base themes, which we’ll tell you more about later in this section.