how to remove white top and Botton border from Android option menu?

Question

How can I remove that white top and Botton border from Android option men. [1]: https://i.stack.imgur.com/5DJBX.jpg

<item
    android:id="@+id/mail"

    android:icon="@drawable/ic_launcher_background"
    android:title="@string/menu"
    android:visible="true" />

    <item android:id="@+id/search_item"
        android:title="Search" />
    <item android:id="@+id/upload_item"
        android:title="Upload" />
    <item android:id="@+id/copy_item"
        android:title="Copy" />
    <item android:id="@+id/print_item"
        android:title="Print" />
    <item android:id="@+id/share_item"
        android:title="Share" />
    <item android:id="@+id/bookmark_item"
        android:title="BookMark" />

[![enter image description here][1]][1]