parsec-vdd/app/Components/CloseButton.xaml

<UserControl
    x:Class="ParsecDisplay.Components.CloseButton"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
    xmlns:local="clr-namespace:ParsecDisplay.Components"
    mc:Ignorable="d" 
    d:DesignHeight="40" d:DesignWidth="60"
    d:Background="Black"
>
    <Button Foreground="White" Content="✕" FontSize="16" Click="Button_Click">
        <Button.Style>
            <Style TargetType="{x:Type Button}">
                <Setter Property="Background" Value="Transparent"/>
                <Setter Property="Template">
                    <Setter.Value>
                        <ControlTemplate TargetType="{x:Type Button}">
                            <Border Background="{TemplateBinding Background}">
                                <ContentPresenter HorizontalAlignment="Center" VerticalAlignment="Center"/>
                            </Border>
                        </ControlTemplate>
                    </Setter.Value>
                </Setter>
                <Style.Triggers>
                    <Trigger Property="IsMouseOver" Value="True">
                        <Setter Property="Background" Value="#4FFF"/>
                    </Trigger>
                    <Trigger Property="IsPressed" Value="True">
                        <Setter Property="Background" Value="#8FFF"/>
                    </Trigger>
                </Style.Triggers>
            </Style>
        </Button.Style>
    </Button>
</UserControl>