[android] How to set dropdown arrow in spinner?

copy and paste this xml instead of your xml

<?xml version="1.0" encoding="UTF-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/back1"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <LinearLayout
        android:id="@+id/linearLayout1"
        android:layout_width="wrap_content"
        android:layout_height="55dp"
        android:layout_alignParentLeft="true"
        android:layout_alignParentRight="true"
        android:layout_alignParentTop="true"
        android:layout_marginTop="20dp" 
        android:background="@drawable/red">

        <Spinner
            android:id="@+id/spinner1"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:dropDownWidth="fill_parent" 
            android:background="@android:drawable/btn_dropdown"
         />

    </LinearLayout>

    <EditText
        android:id="@+id/editText1"
        android:layout_width="wrap_content"
        android:layout_height="55dp"
        android:layout_alignLeft="@+id/linearLayout1"
        android:layout_alignRight="@+id/linearLayout1"
        android:layout_below="@+id/linearLayout1"
        android:layout_marginTop="25dp"
        android:background="@drawable/red"
        android:ems="10"
        android:hint="enter card number" >

        <requestFocus />
    </EditText>

    <LinearLayout
        android:id="@+id/linearLayout2"
        android:layout_width="wrap_content"
        android:layout_height="55dp"
        android:layout_alignLeft="@+id/editText1"
        android:layout_alignRight="@+id/editText1"
        android:layout_below="@+id/editText1"
        android:layout_marginTop="33dp"
        android:orientation="horizontal" 
        android:background="@drawable/red">

        <Spinner
            android:id="@+id/spinner3"
            android:layout_width="72dp"
            android:layout_height="wrap_content"
            android:background="@android:drawable/btn_dropdown"
             />

        <Spinner
            android:id="@+id/spinner2"
            android:layout_width="72dp"
            android:layout_height="wrap_content" 
            android:background="@android:drawable/btn_dropdown"
            />

        <EditText
            android:id="@+id/editText2"
            android:layout_width="22dp"
            android:layout_height="match_parent"
            android:layout_weight="0.18"
            android:ems="10"
            android:hint="enter cvv" />

    </LinearLayout>

    <LinearLayout
        android:id="@+id/linearLayout3"
        android:layout_width="wrap_content"
        android:layout_height="55dp"
        android:layout_alignParentLeft="true"
        android:layout_alignRight="@+id/linearLayout2"
        android:layout_below="@+id/linearLayout2"
        android:layout_marginTop="26dp"
        android:orientation="vertical"
        android:background="@drawable/red" >
    </LinearLayout>

    <Spinner
        android:id="@+id/spinner4"
        android:layout_width="15dp"
        android:layout_height="18dp"
        android:layout_alignBottom="@+id/linearLayout3"
        android:layout_alignLeft="@+id/linearLayout3"
        android:layout_alignRight="@+id/linearLayout3"
        android:layout_alignTop="@+id/linearLayout3"
        android:background="@android:drawable/btn_dropdown"
      />

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentRight="true"
        android:layout_below="@+id/linearLayout3"
        android:layout_marginTop="18dp"
        android:text="Add Amount" 
        android:background="@drawable/buttonsty"/>
</RelativeLayout>