I have downloaded fresh copy of magento version 2.2 and was expecting blank theme or base theme just like we had in previous versions till 1.9 but to my surprise there is no theme at all.
I was looking for themes under app/desgin/frontend/Magento but couldn't find any single theme rather it is empty folder. Any idea?
I am working on my local wamp server on WIN OS.
They are in vendor/magento/theme-frontend-blank and vendor/magento/theme-frontend-luma.
But you can locate your custom theme in app/design folder.
For now, Magento 2 places all its core modules and themes to the vendor/magento folder.