dialog = DatePickerDialog(context!!, R.style.DatePickerDarkDialog, this, year, month, day)

    <!--DatePicker-->
    <style name="DatePickerDarkDialog" parent="Theme.AppCompat.Light.Dialog">
        <item name="colorAccent">@color/primary_color</item>                   <!--header background-->
        <item name="android:windowBackground">@color/default_bg_color</item>     <!--calendar background-->
        <item name="android:colorControlActivated">@color/primary_color</item> <!--selected day-->
        <item name="android:textColorPrimary">@color/secondary_text_color</item> <!--days of the month-->
        <item name="android:textColorSecondary">@color/primary_text_color</item>    <!--days of the week-->
    </style>

   dialog.setOnShowListener {
            dialog.getButton(DatePickerDialog.BUTTON_NEGATIVE).background = null
            dialog.getButton(DatePickerDialog.BUTTON_POSITIVE).background = null
            dialog.getButton(DatePickerDialog.BUTTON_NEUTRAL).background = null

            dialog.getButton(DatePickerDialog.BUTTON_NEGATIVE)
                .setTextColor(ContextCompat.getColor(context!!, R.color.calendar_btn_color))
            dialog.getButton(DatePickerDialog.BUTTON_POSITIVE)
                .setTextColor(ContextCompat.getColor(context!!, R.color.calendar_btn_color))
            dialog.getButton(DatePickerDialog.BUTTON_NEUTRAL)
                .setTextColor(ContextCompat.getColor(context!!, R.color.calendar_btn_color))
        }