android material button designs. https://medium.com/google-developers/choosing-a-button-style-with-purpose-and-intent-35a945e228d3#.v0gg0zvte

layout.xml

<!-- flat style used on dialogs -->
<Button
  android:id="@+id/my_flat_button"
  android:layout_width="wrap_content"
  android:layout_height="match_parent"
  android:text="@string/flat"
  android:textAppearance="@style/TextAppearance.AppCompat.Button"
  android:textColor="@color/app_body_text"
  style="?borderlessButtonStyle" />
  
<!-- raised button -->
<Button
  android:id="@+id/my_raised_button"
  android:layout_width="wrap_content"
  android:layout_height="match_parent"
  android:text="@string/raised"
  android:textAppearance="@style/TextAppearance.AppCompat.Button"
  android:textColor="@color/app_body_text"
  style="@style/Widget.AppCompat.Button.Colored" />

<!-- floating -->
<android.support.design.widget.FloatingActionButton
  android:id="@+id/my_fab_button"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:src="@drawable/fab_icon"
  app:fabSize="mini" />