android - Alertdialog shows background three times on old devices -

i'm trying make dialog custom style. on android 5 works: http://i.stack.imgur.com/y7zsg.png

but on older devices happens: http://i.stack.imgur.com/uixur.png

styles.xml:

<resources> <style name="apptheme" parent="theme.appcompat.noactionbar">     <item name="android:textcolorprimary">#ffffff</item>     <item name="android:alertdialogtheme">@style/popupdialog</item> </style>  <style name="popupdialog" parent="theme.appcompat.dialog">     <item name="android:textcolorprimary">#ffffff</item>     <item name="android:background">@drawable/background_dialog</item>     <item name="android:windowbackground">@android:color/transparent</item> </style> </resources> 

background_dialog.xml:

<?xml version="1.0" encoding="utf-8"?> <shape xmlns:android="http://schemas.android.com/apk/res/android" android:shape="rectangle">     <corners android:bottomrightradius="10dp" android:bottomleftradius="10dp"         android:topleftradius="10dp" android:toprightradius="10dp"/>     <solid android:color="#7b8f8a"/> </shape> 

i tried many things nothing seems work.