NumberSystem/numbersystem/MainWindow.xaml

<Window x:Class="numbersystem.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:numbersystem"
        mc:Ignorable="d"
        Title="Система счислений" Height="550" Width="350" ResizeMode="NoResize" Icon="/icon.png" FontFamily="Montserrat Light">
    <Window.Resources>
        <Style TargetType="Button">
            <Setter Property="ItemsControl.Background" Value="#8888d7"/>
            <Setter Property="ItemsControl.Foreground" Value="White"/>
            <Setter Property="ItemsControl.Margin" Value="10"/>
        </Style>
    </Window.Resources>
    <Grid>
        <TabControl>
            <TabItem Header="Калькулятор" FontFamily="Montserrat Light">
                <Grid Background="#d7d7f2">
                    <Grid.RowDefinitions>
                        <RowDefinition/>
                        <RowDefinition/>
                        <RowDefinition/>
                        <RowDefinition/>
                        <RowDefinition/>
                        <RowDefinition/>
                        <RowDefinition/>
                        <RowDefinition/>
                    </Grid.RowDefinitions>
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition/>
                        <ColumnDefinition/>
                        <ColumnDefinition/>
                        <ColumnDefinition/>
                    </Grid.ColumnDefinitions>
                    <TextBox IsReadOnly="True" Grid.Row="0" Grid.ColumnSpan="4" Margin="10" 
                             FontSize="16" HorizontalScrollBarVisibility="Auto" 
                             VerticalContentAlignment="Center" HorizontalContentAlignment="Right"/>
                    <Label Content="Выберите СС:" Grid.Row="1" Grid.ColumnSpan="2" Margin="10,10,43,10" FontSize="14"/>
                    <ComboBox Margin="48,10,10,30" Grid.ColumnSpan="3" Grid.Column="1" Grid.Row="1">
                        <TextBlock Text="Двоичная"/>
                        <TextBlock Text="Троичная"/>
                        <TextBlock Text="Восьмеричная"/>
                        <TextBlock Text="Шестнадцатиричная"/>
                    </ComboBox>
                    <Button Content="CA" Grid.Row="5" Grid.Column="0"/>
                    <Button Content="0" Grid.Row="5" Grid.Column="1"/>
                    <Button Content="⌫" Grid.Row="5" Grid.Column="2"/>
                    <Button Content="1" Grid.Row="4" Grid.Column="0"/>
                    <Button Content="2" Grid.Row="4" Grid.Column="1"/>
                    <Button Content="3" Grid.Row="4" Grid.Column="2"/>
                    <Button Content="4" Grid.Row="3" Grid.Column="0"/>
                    <Button Content="5" Grid.Row="3" Grid.Column="1"/>
                    <Button Content="6" Grid.Row="3" Grid.Column="2"/>
                    <Button Content="7" Grid.Row="2" Grid.Column="0"/>
                    <Button Content="8" Grid.Row="2" Grid.Column="1"/>
                    <Button Content="9" Grid.Row="2" Grid.Column="2"/>
                    <Button Content="A" Grid.Row="6" Grid.Column="0" Background="#6c6cdf"/>
                    <Button Content="B" Grid.Row="6" Grid.Column="1" Background="#6c6cdf"/>
                    <Button Content="C" Grid.Row="6" Grid.Column="2" Background="#6c6cdf"/>
                    <Button Content="D" Grid.Row="7" Grid.Column="0" Background="#6c6cdf"/>
                    <Button Content="E" Grid.Row="7" Grid.Column="1" Background="#6c6cdf"/>
                    <Button Content="F" Grid.Row="7" Grid.Column="2" Background="#6c6cdf"/>
                    <Button Content="+" Grid.Row="2" Grid.Column="3" Background="#4040bf"/>
                    <Button Content="-" Grid.Row="3" Grid.Column="3" Background="#4040bf"/>
                    <Button Content="×" Grid.Row="4" Grid.Column="3" Background="#4040bf"/>
                    <Button Content="÷" Grid.Row="5" Grid.Column="3" Background="#4040bf"/>
                    <Button Content="%" Grid.Row="6" Grid.Column="3" Background="#4040bf"/>
                    <Button Content="=" Grid.Row="7" Grid.Column="3" Background="#4040bf"/>
                </Grid>
            </TabItem>
            <TabItem Header="История" FontFamily="Montserrat Light">
                <Grid Background="#d7d7f2"/>
            </TabItem>
            <TabItem Header="Диаграмма" FontFamily="Montserrat Light">
                <Grid Background="#d7d7f2"/>
            </TabItem>
        </TabControl>

    </Grid>
</Window>