WPF CheckBox ControlTemplate IsChecked inner and content color changed

//xaml
<Window x:Class="WpfApp133.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp133"
        mc:Ignorable="d"
        Title="MainWindow" Height="150" Width="450">
    <Window.Resources>
        <Style TargetType="{x:Type CheckBox}" x:Key="cbxStyle">
            <Setter Property="IsChecked" Value="{Binding IsCbxChecked,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"/>
            <Setter Property="Content" Value="{Binding CbxContent,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"/>
            <Setter Property="IsThreeState" Value="False"/>
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type CheckBox}">
                        <Grid>
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition/>
                                <ColumnDefinition Width="3*"/>
                            </Grid.ColumnDefinitions>
                            <Ellipse Grid.Column="0"
                          Fill="Cyan"
                          Width="30"
                          Height="30"/>
                            <Ellipse Grid.Column="0"
                          x:Name="innerElp" 
                          Width="15"
                          Height="15"
                          Fill="Red"
                          Visibility="Collapsed"/>
                            <TextBlock Grid.Column="1"
                                       x:Name="tbk"
                                       VerticalAlignment="Center"
                                       Text="{TemplateBinding Content}"/>
                        </Grid>
                        <ControlTemplate.Triggers>
                            <Trigger Property="IsChecked" Value="True">
                                <Setter TargetName="innerElp" Property="Visibility" Value="Visible"/>
                                <Setter TargetName="tbk" Property="Foreground" Value="Red"/>
                                <Setter TargetName="tbk" Property="FontWeight" Value="ExtraBold"/>
                            </Trigger>
                        </ControlTemplate.Triggers>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </Window.Resources>
    <Grid>
        <CheckBox Style="{StaticResource cbxStyle}" />
    </Grid>
</Window>



//cs
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace WpfApp133
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window, INotifyPropertyChanged
    {
        int idx = 0;
        public MainWindow()
        {
            InitializeComponent();
            this.DataContext = this;
            this.Loaded += MainWindow_Loaded;
        }

        private void MainWindow_Loaded(object sender, RoutedEventArgs e)
        {
            Thread t1 = new Thread(() =>
            {
                while(true)
                {
                    CbxContent = $"{++idx}____{Guid.NewGuid().ToString("N")}";
                    IsCbxChecked = idx % 2 == 0;
                    Thread.Sleep(1000);
                }
            });
            t1.Start();
        }

        public event PropertyChangedEventHandler PropertyChanged;
        private void OnPropertyChanged([CallerMemberName] string propName = "")
        {
            var handler = PropertyChanged;
            if (handler != null)
            {
                handler?.Invoke(this, new PropertyChangedEventArgs(propName));
            }
        }

        private bool isCbxChecked;
        public bool IsCbxChecked
        {
            get
            {
                return isCbxChecked;
            }
            set
            {
                if(value!=isCbxChecked)
                {
                    isCbxChecked = value;
                    OnPropertyChanged(nameof(IsCbxChecked));
                }
            }
        }

        private string cbxContent;
        public string CbxContent
        {
            get
            {
                return cbxContent;
            }
            set
            {
                if(value != cbxContent)
                {
                    cbxContent = value;
                    OnPropertyChanged(nameof(CbxContent));
                }
            }
        }
    }
}