lab4/WpfApp3/dark.xaml

<ResourceDictionary 
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:WpfApp3">
    <Style 
        x:Key="TextBlockStyle" 
        TargetType="TextBlock">
        <Setter 
            Property="Background" 
            Value="Gray" />
        <Setter 
            Property="Foreground" 
            Value="White" />
    </Style>
    <Style 
        x:Key="WindowStyle" 
        TargetType="Window">
        <Setter 
            Property="Background" 
            Value="Gray" />
    </Style>
    <Style 
        x:Key="ButtonStyle" 
        TargetType="Button">
        <Setter 
            Property="Background" 
            Value="Gray" />
        <Setter 
            Property="Foreground" 
            Value="White" />
        <Setter 
            Property="BorderBrush" 
            Value="White" />
    </Style>
</ResourceDictionary>