android-calculatorpp/app/src/main/res/drawable/blue_button_shape.xml

<?xml version="1.0" encoding="utf-8"?>

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<inset xmlns:a="http://schemas.android.com/apk/res/android"
    a:insetBottom="@dimen/cpp_button_padding"
    a:insetLeft="@dimen/cpp_button_padding"
    a:insetRight="@dimen/cpp_button_padding"
    a:insetTop="@dimen/cpp_button_padding">
    <shape>
        <gradient
            a:angle="90"
            a:endColor="#003481"
            a:startColor="#001c45" />
        <corners a:radius="0dp" />
    </shape>
</inset>