drawable文件下创建即可
<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">
<gradient
android:centerColor="#3087ea"
android:startColor="#80ccffcc"
android:endColor="#80cccccc"></gradient>
<corners android:radius="15dp"></corners>
</shape>