Custom control's name is not recognized in application's namespace

Question

I'm making a simple navigation control in WPF by following this tutorial. But for some reason it name doesn't exist in the namespace.

The errors, sorry they're in Polish:

Can someone explain where I made a mistake?

Custom control's C# file:

namespace WPFBattleCalculator
{
    
    public class NavButton : ButtonBase
    {
        static NavButton()
        {
            DefaultStyleKeyProperty.OverrideMetadata(typeof(NavButton), new FrameworkPropertyMetadata(typeof(NavButton)));

        }
        public static readonly DependencyProperty TextProperty = DependencyProperty.Register("Text", typeof(string), typeof(NavButton), new PropertyMetadata(null));
        public static readonly DependencyProperty UriProperty = DependencyProperty.Register("Uri", typeof(Uri), typeof(NavButton), new PropertyMetadata(null));
        public string Text
        {
            get { return (string)GetValue(TextProperty); }
            set { SetValue(TextProperty, value); }
        }
        public Uri NavUri
        {
            get { return (Uri)GetValue(UriProperty); }
            set { SetValue(UriProperty, value); }
        }


    }
}

Custom control's XAML file:

<ResourceDictionary
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:WPFBattleCalculator">


    <Style TargetType="{x:Type local:NavButton}">
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type local:NavButton}">
                    <Border Background="{TemplateBinding Background}"
                            BorderBrush="{TemplateBinding BorderBrush}"
                            BorderThickness="{TemplateBinding BorderThickness}">
                        <TextBlock HorizontalAlignment="Center" VerticalAlignment="Center" Text="{TemplateBinding Text}" TextWrapping="Wrap" Margin="5"/>
                    </Border>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
</ResourceDictionary>

I mainly tried searching in the tutorial if I skipped anything, but the only thing I skipped is the image property and some XAML beacuse I didn't need them.