Style android spinner

Remove the SpinnerStyle background attribute.

Remove this:

<style name="spinnerStyle">
    <item name="android:background">@drawable/whitish_rectangle</item>
</style>

which is what draws the background white rectangle.

Building on the code in your question, here is a basic example on how you can style your Spinner:

The styles.xml file sets styles for the SpinnerItem and SpinnerDropDownItem:

<resources>
    <style name="customtheme" parent="@android:style/Theme.Light">
        <item name="android:spinnerItemStyle">@style/SpinnerItem</item>
        <item name="android:spinnerDropDownItemStyle">@style/SpinnerDropDownItem</item>
    </style>
    <style name="SpinnerItem">
        <item name="android:textColor">#993399</item>
        <item name="android:background">@drawable/my_rectangle</item>
    </style>
    <style name="SpinnerDropDownItem">
        <item name="android:textColor">#993399</item>
        <item name="android:background">@drawable/my_rectangle</item>
    </style>
</resources>

For testing, I’ve created a bright-colored drawable shape, called my_rectangle.xml. Replace this with your own drawable:

<?xml version="1.0" encoding="UTF-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android" >
    <solid android:color="#ff0000" />
    <stroke
        android:width="1dp"
        android:color="#888888" />
</shape>

Add the Spinner to the Activity's layout:

<LinearLayout 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:padding="40dip">
    <Spinner
        android:id="@+id/edit_countrySpinner"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:entries="@array/location_names"/>
</LinearLayout>

This produces:

with no white square in the background.