You are placing the solid shape item over the gradient shape item.
You need to add some padding to the gradient shape. You are doing the opposite adding the padding to the solid shape versus the gradient shape, try this:
<layer-list xmlns:android="http://schemas.android.com/apk/res/android" >
<item>
<shape android:shape="rectangle" >
<solid android:color="#ff8898A4" />
</shape>
</item>
<item android:bottom="10dp">
<shape android:shape="rectangle" >
<gradient
android:angle="90"
android:endColor="#ffD6DDD8"
android:startColor="#ffB1BBC3" />
</shape>
</item>
</layer-list>