<Window x:Class="RP.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:RP"
        Title="MainWindow" Height="450" Width="525">
    <Window.Resources>
        <Style x:Key="RoundCorner" TargetType="{x:Type local:ChartButton}">
        ...

    public class ChartButton : ToggleButton
    {
        ...
    }

    public partial class MainWindow
    {
        public MainWindow()
        {
            var style = FindResource("RoundCorner") as Style;
            ...
            InitializeComponent();
        }
    }

    public partial class MainWindow
    {
        public MainWindow()
        {
            InitializeComponent();
            Chart.Children.Add(new PGrid());
            Chart2.Children.Add(new PGrid());

    public partial class MainWindow
    {
        private PokerGrid Pg1;
        private PokerGrid Ppg2;
        public MainWindow()
        {
            Pg1 = new PGrid();
            Pg2 = new PGrid();
            InitializeComponent();
            Chart.Children.Add(Pg1);
            Chart2.Children.Add(Pg2);

public PGrid()
        {
            InitializeComponent();
        }

        void InitializeComponent()
        {
            // Добавляем кнопки
            Elements = new Dictionary<string, FrameworkElement>();
            var style = Application.Current.MainWindow.TryFindResource("RoundCorner") as Style;