Figured out how to expand controls to fill parent. yay

windows/WinUI/MainWindow.xaml

@@ -99,8 +99,14 @@
                 </Grid>
             </TabItem>
             <TabItem x:Name="Peers" Header="Peers" Background="#FF234447" Foreground="White">
-                <Grid Background="#FFE5E5E5" HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
-                    <local:PeersPage x:Name="peersPage" HorizontalAlignment="Stretch" VerticalAlignment="Stretch"></local:PeersPage>
+                <Grid Background="#FFE5E5E5" HorizontalAlignment="Left" VerticalAlignment="Top">
+                    <Grid.ColumnDefinitions>
+                        <ColumnDefinition Width="*"/>
+                    </Grid.ColumnDefinitions>
+                    <Grid.RowDefinitions>
+                        <RowDefinition Height="*"/>
+                    </Grid.RowDefinitions>
+                    <local:PeersPage x:Name="peersPage" HorizontalAlignment="Left" VerticalAlignment="Top" Grid.Column="0" Grid.Row="0"/>
                 </Grid>
             </TabItem>
 		</TabControl>

windows/WinUI/MainWindow.xaml.cs

@@ -35,6 +35,7 @@ namespace WinUI
 
             updateStatus();
             updateNetworks();
+            updatePeers();
 
             DataObject.AddPastingHandler(joinNetworkID, OnPaste);
 

windows/WinUI/NetworksPage.xaml

@@ -5,7 +5,7 @@
              xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
              mc:Ignorable="d" 
              d:DesignHeight="300" d:DesignWidth="300">
-    <ScrollViewer x:Name="MyScrollViewer" HorizontalScrollBarVisibility="Disabled" VerticalScrollBarVisibility="Auto"  HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
+    <ScrollViewer x:Name="MyScrollViewer" HorizontalScrollBarVisibility="Disabled" VerticalScrollBarVisibility="Auto"  HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Width="{Binding RelativeSource={RelativeSource AncestorType={x:Type Window}}, Path=ActualWidth}" Height="{Binding RelativeSource={RelativeSource AncestorType={x:Type Window}}, Path=ActualHeight}">
         <WrapPanel x:Name="wrapPanel" Background="#FF555555"  HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
 
         </WrapPanel>

windows/WinUI/PeersPage.xaml

@@ -5,7 +5,7 @@
              xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
              mc:Ignorable="d" 
              d:DesignHeight="300" d:DesignWidth="300" Background="White" Foreground="Black">
-    <DataGrid x:Name="dataGrid" AutoGenerateColumns="False" CanUserResizeColumns="True" Margin="0,0,0,0" CanUserReorderColumns="False">
+    <DataGrid x:Name="dataGrid" AutoGenerateColumns="False" CanUserResizeColumns="True" Margin="0,0,0,0" CanUserReorderColumns="False" Width="{Binding RelativeSource={RelativeSource AncestorType={x:Type Window}}, Path=ActualWidth}" Height="{Binding RelativeSource={RelativeSource AncestorType={x:Type Window}}, Path=ActualHeight}">
         <DataGrid.Columns>
             <DataGridTextColumn Header="Address" Binding="{Binding Address}"/>
             <DataGridTextColumn Header="Version" Binding="{Binding VersionString}"/>