packages/SystemUI/res/layout/system_bar_notification_peek.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
/* apps/common/assets/default/default/skins/StatusBar.xml
**
** Copyright 2006, The Android Open Source Project
**
** Licensed under the Apache License, Version 2.0 (the "License"); 
** you may not use this file except in compliance with the License. 
** You may obtain a copy of the License at 
**
**     http://www.apache.org/licenses/LICENSE-2.0 
**
** Unless required by applicable law or agreed to in writing, software 
** distributed under the License is distributed on an "AS IS" BASIS, 
** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
** See the License for the specific language governing permissions and 
** limitations under the License.
*/
-->

<!--    android:background="@drawable/system_bar_closed_default_background" -->
<com.android.systemui.statusbar.tablet.NotificationPeekPanel
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_height="wrap_content"
    android:layout_width="match_parent"
    android:background="@*android:drawable/dialog_full_holo_dark"
    android:orientation="vertical"
    >

    <FrameLayout 
        android:id="@+id/content"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center_horizontal|bottom"
        android:animationCache="false"
        android:orientation="vertical"
        android:background="@drawable/system_bar_background"
        android:clickable="true"
        android:focusable="true"
        android:descendantFocusability="afterDescendants"
        >
    </FrameLayout>
</com.android.systemui.statusbar.tablet.NotificationPeekPanel>