自定义ActionBar背景（分别针对3.0以下和3.0以上的版本）

<?xml version="1.0" encoding="utf-8"?>
<resources xmlns:android="http://schemas.android.com/apk/res/android">

    <style name="CustomActionBarTheme" parent="@android:style/Theme.Holo.Light.DarkActionBar">
        <item name="android:actionBarStyle">@style/CustomBackground</item>
    </style>

    <style name="CustomBackground" parent="@android:style/Widget.Holo.Light.ActionBar.Solid.Inverse">
        <item name="android:background">@drawable/actionbar_background</item>
    </style>
    
    <style 
        name="CustomActionBarOverlayTheme"
        parent="@android:style/Theme.Holo"
        >
        <item name="android:windowActionBarOverlay">true</item>
        
    </style>

</resources>

<?xml version="1.0" encoding="utf-8"?>
<resources>
    
    <style name="CustomActionBarTheme" parent="@style/Theme.AppCompat.Light.DarkActionBar">
        <item name="actionBarStyle">@style/CustomBackground</item>
    </style>

    <style name="CustomBackground" parent="@style/Widget.AppCompat.Light.ActionBar.Solid.Inverse">
        <item name="background">@drawable/actionbar_background</item>
    </style>
    
    <style 
        name="CustomActionBarOverlayTheme"
        parent="@style/Theme.AppCompat"
        >
        <item name="windowActionBarOverlay">true</item>
        
    </style>
    
</resources>