This module prints hierarchy tree for all themes installed in m2 instance.
composer require --dev fetchtex/theme-hierarchy-tree
bin/magento module:enable Fetchtex_ThemeHierarchyTree
bin/magento setup:upgrade
bin/magento theme:tree
Sample output:
.
│
├── Magento/blank
│ ├── Magento/luma
│ └── Customer/fashion
│ ├── Custom/fashion_shoe
└── Magento/backend