The multiple themes help to give extra looks and effect on website on special days or festival while preserving normal non-seasonal store design in back side. And this all can be done by simple modification on design without writing whole new theme for this.

Magento handles loading multiple themes by assigning something called hierarchy to the themes which is simply a process of cancelling out redundant files to load only that which has highest priorirty in hierarchy.

Magento has always used fall-back logic to find themes in hierarchy. The order of fall-back hierarchy in magento v 1.4+ is as follows:

Magento Theme Hierarchy and Fall Back Condition

  1. First look for requested file in :
    • app/design/frontend/custom_package/custom_theme/
    • skin/frontend/custom_package/custom_theme/
  2. If not found then search in :
    • app/design/frontend/custom_package/default/
    • skin/frontend/custom_package/default/
  3. If not found then search in :
    • app/design/frontend/base/default/
    • skin/frontend/base/default/
  4. If not found then error message will be displayed.