frameworks/base/core/res/res/values/Style.xml

WindowTitleBackground就是Acitity背景

<style name="WindowTitleBackground">
        <item name="android:background">#FF194A78</item>
    </style>

    <style name="WindowTitle">
        <item name="android:singleLine">true</item>
        <item name="android:textAppearance">@style/TextAppearance.WindowTitle</item>
        <item name="android:shadowColor">#BB000000</item>
        <item name="android:shadowRadius">2.75</item>
    </style>

    <style name="DialogWindowTitle">
        <item name="android:maxLines">1</item>
        <item name="android:scrollHorizontally">true</item>
        <item name="android:textAppearance">@style/TextAppearance.DialogWindowTitle</item>
    </style>