My <ContentPage.Content> in Xamarin.Forms is not showing up? - xamarin.forms

Question

When I add toolbar in my Main Page the content page disappear. What should I do to fix this? Can you share insight or point me to links for me to learn. I am just starting with xamarin forms. I been finding the answer the whole day but I can't find one.
<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:local="clr-namespace:KLConnect"
x:Class="KLConnect.MainPage"
Title="KLConnect TTM+ Operation">
<Label x:Name="label"
FontSize="Medium"
VerticalOptions="Center"
HorizontalOptions="Center" />
<ContentPage.ToolbarItems>
<ToolbarItem Text="setting"
Order="Primary"
Clicked="OnToolbarItemClicked">
<ToolbarItem.Icon>
<OnPlatform x:TypeArguments="FileImageSource"
Android="ic_build_white_48dp.png"/>
</ToolbarItem.Icon>
</ToolbarItem>
<ToolbarItem Text="close"
Order="Primary"
Clicked="OnToolbarItemClicked">
<ToolbarItem.Icon>
<OnPlatform x:TypeArguments="FileImageSource"
Android="ic_highlight_off_white_48dp.png"/>
</ToolbarItem.Icon>
</ToolbarItem>
<ToolbarItem Text="help"
Order="Primary"
Clicked="OnToolbarItemClicked">
<ToolbarItem.Icon>
<OnPlatform x:TypeArguments="FileImageSource"
Android="ic_help_outline_white_48dp.png"/>
</ToolbarItem.Icon>
</ToolbarItem>
</ContentPage.ToolbarItems>
<ContentPage.Resources>
<ResourceDictionary>
<Style x:Key="plainButton" TargetType="Button">
<Setter Property="BackgroundColor" Value="#eee"/>
<Setter Property="TextColor" Value="Black" />
<Setter Property="BorderRadius" Value="0"/>
<Setter Property="FontSize" Value="40" />
</Style>
<Style x:Key="darkerButton" TargetType="Button">
<Setter Property="BackgroundColor" Value="#ddd"/>
<Setter Property="TextColor" Value="Black" />
<Setter Property="BorderRadius" Value="0"/>
<Setter Property="FontSize" Value="40" />
</Style>
<Style x:Key="orangeButton" TargetType="Button">
<Setter Property="BackgroundColor" Value="#E8AD00"/>
<Setter Property="TextColor" Value="White" />
<Setter Property="BorderRadius" Value="0"/>
<Setter Property="FontSize" Value="40" />
</Style>
</ResourceDictionary>
</ContentPage.Resources>
<ContentPage.Content>
<Grid x:Name="controlGrid" RowSpacing="1" ColumnSpacing="1">
<Grid.RowDefinitions>
<RowDefinition Height="150" />
<RowDefinition Height="*" />
<RowDefinition Height="*" />
<RowDefinition Height="*" />
<RowDefinition Height="*" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*" />
<ColumnDefinition Width="*" />
<ColumnDefinition Width="*" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<Label Text="0" Grid.Row="0" HorizontalTextAlignment="End" VerticalTextAlignment="End" TextColor="White"
FontSize="60" Grid.ColumnSpan="4" />
<Button Text = "C" Grid.Row="1" Grid.Column="0"
Style="{StaticResource darkerButton}" />
<Button Text = "+/-" Grid.Row="1" Grid.Column="1"
Style="{StaticResource darkerButton}" />
<Button Text = "%" Grid.Row="1" Grid.Column="2"
Style="{StaticResource darkerButton}" />
<Button Text = "div" Grid.Row="1" Grid.Column="3"
Style="{StaticResource orangeButton}" />
<Button Text = "7" Grid.Row="2" Grid.Column="0"
Style="{StaticResource plainButton}" />
<Button Text = "8" Grid.Row="2" Grid.Column="1"
Style="{StaticResource plainButton}" />
<Button Text = "9" Grid.Row="2" Grid.Column="2"
Style="{StaticResource plainButton}" />
<Button Text = "X" Grid.Row="2" Grid.Column="3"
Style="{StaticResource orangeButton}" />
<Button Text = "4" Grid.Row="3" Grid.Column="0"
Style="{StaticResource plainButton}" />
<Button Text = "5" Grid.Row="3" Grid.Column="1"
Style="{StaticResource plainButton}" />
<Button Text = "6" Grid.Row="3" Grid.Column="2"
Style="{StaticResource plainButton}" />
<Button Text = "-" Grid.Row="3" Grid.Column="3"
Style="{StaticResource orangeButton}" />
<Button Text = "1" Grid.Row="4" Grid.Column="0"
Style="{StaticResource plainButton}" />
<Button Text = "2" Grid.Row="4" Grid.Column="1"
Style="{StaticResource plainButton}" />
<Button Text = "3" Grid.Row="4" Grid.Column="2"
Style="{StaticResource plainButton}" />
<Button Text = "+" Grid.Row="4" Grid.Column="3"
Style="{StaticResource orangeButton}" />
<Button Text = "0" Grid.ColumnSpan="2"
Grid.Row="5" Grid.Column="0" Style="{StaticResource plainButton}" />
<Button Text = "." Grid.Row="5" Grid.Column="2"
Style="{StaticResource plainButton}" />
<Button Text = "=" Grid.Row="5" Grid.Column="3"
Style="{StaticResource orangeButton}" />
</Grid>
</ContentPage.Content>
</ContentPage>

Answer 1

It's because you have a Label already set at the beginning of your xaml.
Remove this
<Label x:Name="label"
FontSize="Medium"
VerticalOptions="Center"
HorizontalOptions="Center" />