A PleasantUI-styled DatePicker that decouples the visual container from the internal flyout button, allowing full theme control over the outer shape. The template must provide a click area and a hidden flyout button for Avalonia's internal wiring.

<PleasantDatePicker Watermark="Select a date" />

Inherits all properties from DatePicker:

• SelectedDate - The currently selected date
• Watermark - Placeholder text shown when no date is selected
• MinYear - Minimum year that can be selected
• MaxYear - Maximum year that can be selected
• IsTodayHighlighted - Whether today's date is highlighted in the calendar
• DisplayDate - The date to display in the calendar view
• And other standard DatePicker properties

The control template must provide:

• PART_ClickArea - The visible, styled container that the user clicks
• PART_FlyoutButton - A hidden zero-size Button kept for Avalonia's internal wiring

<PleasantDatePicker Watermark="Select a date"
                   SelectedDate="{Binding BirthDate}" />

Restrict selectable dates:

<PleasantDatePicker MinYear="1900"
                   MaxYear="2100" />

Control whether today's date is highlighted:

<PleasantDatePicker IsTodayHighlighted="True" />

Bind to a DateTime property:

<PleasantDatePicker SelectedDate="{Binding SelectedDate, Mode=TwoWay}" />

public DateTime? SelectedDate
{
    get => _selectedDate;
    set
    {
        _selectedDate = value;
        OnPropertyChanged();
    }
}

<StackPanel Spacing="12" Width="250">
    <TextBlock Text="Date Selection" FontWeight="Bold" />
    
    <PleasantDatePicker Watermark="Start date"
                       SelectedDate="{Binding StartDate}" />
    
    <PleasantDatePicker Watermark="End date"
                       SelectedDate="{Binding EndDate}"
                       MinYear="2020"
                       MaxYear="2030" />
</StackPanel>

• The control uses a custom click area to trigger the calendar popup, allowing complete control over the visual styling
• The internal flyout button is kept in the visual tree (zero size) to maintain Avalonia's DatePicker functionality