Translucent Activity filling the entire screen

Question

I'd like to have an activity (2) with translucent aspect over another activity (1), aligned at the top of the screen (4).

I have tried assigning these themes to activity number 2:

<style name="Theme.CustomDialog" parent="android:style/Theme.Dialog">
    <item name="android:windowBackground">@android:color/black</item>
</style>  

<style name="CustomTheme">
    <item name="android:windowBackground">@android:color/transparent</item>
    <item name="android:background">@android:color/transparent</item>
    <item name="android:windowIsFloating">true</item>
    <item name="android:windowNoTitle">true</item>
</style>    

But the result is always 3.

If I set <item name="android:windowIsFloating">false</item> in the CustomTheme the result is 2.

Can anybody tell me how can I get 4? Thanks!

UPDATE: This is my activity 2 layout:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" android:background="#0000">

    <RelativeLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content" android:background="#FFFFFF">

        <Button
            android:id="@+id/button1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Menu" android:layout_centerHorizontal="true"/>

    </RelativeLayout>

</RelativeLayout>

Answer 1

Finally, this theme worked to get a result like image number 4:

  <style name="Theme.CustomTranslucent" parent="android:style/Theme.Translucent">
        <item name="android:backgroundDimEnabled">true</item>
        <item name="android:backgroundDimAmount">0.5</item>
        <item name="android:windowAnimationStyle">@android:style/Animation.Dialog</item>
        <item name="android:background">@android:color/transparent</item>
 </style>  

In my activity 2 layout, I could eihter set android:background="@android:color/transparent" or not set any value at all to make it work.

Thanks to MikeIsrael and Veer for their help.