update

app/src/main/res/drawable/bg_popup_menu.xml

@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="utf-8"?>
+<shape xmlns:android="http://schemas.android.com/apk/res/android"
+       android:shape="rectangle">
+
+    <solid android:color="@color/background_menu"/>
+
+    <corners android:radius="2dp"/>
+
+</shape>

app/src/main/res/values/styles.xml

@@ -67,7 +67,7 @@
     </style>
 
     <style name="Style.PopupMenu" parent="Widget.AppCompat.PopupMenu">
-        <item name="android:popupBackground">@color/background_menu</item>
+        <item name="android:popupBackground">@drawable/bg_popup_menu</item>
     </style>