The design on every app that is in the showcase.....
But, You can explore "modern" design using material themes ....
There are some demos:
AppCompatCollapsingToolbarDemo1
AppCompatContinuousScrollableImageViewDemo1
AppCompatFloatingButtonDemo1
AppCompatNavigationDrawerDemo1
AppCompatNavigationDrawerDemo2
AppCompatRecyclerViewDemo1
AppCompatRecyclerViewDemo2
AppCompatTabLayoutDemo1
AppCompatTabLayoutDemo2
AppCompatViewPagerDemo1
.....