Where can I find all Android built in themes

Android Studio has a Theme Editor which provides preview function.

User can find all built-in themes inside.

2 ways to open it:

1. Open a styles XML file, for instance res/values/styles.xml. Then click Open editor near the top-right of file-editing window.
2. in top menu bar Tools-Android-Theme Editor.

You can see all the theme names in the manifest.xml. For this see the following snapshot:

Your IDE (I know Android Studio does), should show you them.

Otherwise, here they are in raw xml form. https://android.googlesource.com/platform/frameworks/base/+/refs/heads/master/core/res/res/values/themes.xml

More information on Android Dev docs: http://developer.android.com/guide/topics/ui/themes.html