From the docs
If the current theme is derived from Theme
the widget presents the current value as an editable input field with an increment button above and a decrement button below. Long pressing the buttons allows for a quick change of the current value. Tapping on the input field allows to type in a desired value.
So you will need to set the theme. Define styles in styles.xml
<style name="cust_dialog" parent="@android:style/Theme.NoTitleBar.Fullscreen" />
To set the theme follow David's answer @