https://ddangeun.tistory.com/154
Spinner PopUp 디자인 커스텀
<Spinner
android:id="@+id/spinner"
android:layout_width="50dp"
android:layout_height="wrap_content"
android:layout_marginTop="20dp"
android:overlapAnchor="false"
android:popupBackground="@drawable/rect_spinner"
android:popupElevation="10dp"
android:textColor="#CCFFFFFF"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
Spinner PopUp 내부, 항목 디자인 커스텀