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

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

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<selector xmlns:a="http://schemas.android.com/apk/res/android">

    <item a:drawable="@drawable/material_button_pressed" a:state_pressed="true" />

    <item>
        <shape>
            <solid a:color="@color/grey_800" />
        </shape>
    </item>

</selector>