I am trying to define a shape in an XML doc as follows:

```
<shape xmlns:android="http://schemas.android.com/apk/res/android"
  android:shape="rectangle">
  <gradient android:startColor="#FFFFFF" 
    android:endColor="#00FF00"
    android:angle="270" />
  <corners android:radius="3dp" />
  <stroke android:width="5px" android:color="#000000" />
</shape>

```

However, I get the following warnings and errors:

1. Layout width and height to be defined (no example shows these as
being defined)
2. Element corners not allowed here
3. element stroke not allowed here

How can I clear these errors?