Change Spinner dropdown icon

Try applying following style to your spinner using

style="@style/SpinnerTheme"

//Spinner Style:

<style name="SpinnerTheme" parent="android:Widget.Spinner">
    <item name="android:background">@drawable/bg_spinner</item>
</style>

//bg_spinner.xml Replace the arrow_down_gray with your arrow

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">

    <item>

        <layer-list>

            <item>
                <shape>
                    <gradient android:angle="90" android:endColor="#ffffff" android:startColor="#ffffff" android:type="linear" />

                    <stroke android:width="0.33dp" android:color="#0fb1fa" />

                    <corners android:radius="0dp" />

                    <padding android:bottom="3dp" android:left="3dp" android:right="3dp" android:top="3dp" />
                </shape>
            </item>

            <item android:right="5dp">

                <bitmap android:gravity="center_vertical|right" android:src="@drawable/arrow_down_gray" />

            </item>

        </layer-list>

    </item>

</selector>