Android gradient drawable for alert screens...

border-gradient.xml

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <!--  left shadow -->
    <item>
        <shape android:shape="rectangle">
            <gradient
                android:angle="180"
                android:centerColor="#00FF0000"
                android:centerY="0.05"
                android:endColor="#00FF0000"
                android:startColor="#80FF0000" />
        </shape>
    </item>

    <!--  right shadow -->
    <item>
        <shape android:shape="rectangle">
            <gradient
                android:angle="360"
                android:centerColor="#00FF0000"
                android:centerY="0.05"
                android:endColor="#00FF0000"
                android:startColor="#80FF0000" />
        </shape>
    </item>

    <!--  top shadow -->
    <item>
        <shape android:shape="rectangle">
            <gradient
                android:angle="270"
                android:centerColor="#00FF0000"
                android:centerY="0.05"
                android:endColor="#00FF0000"
                android:startColor="#80FF0000" />
        </shape>
    </item>

    <!--  bottom shadow -->
    <item>
        <shape android:shape="rectangle">
            <gradient
                android:angle="90"
                android:centerColor="#00FF0000"
                android:centerY="0.05"
                android:endColor="#00FF0000"
                android:startColor="#80FF0000" />
        </shape>
    </item>
</layer-list>