WithMultipleTextBoxes.xaml

<UserControl x:Class="MaterialDesignThemes.UITests.Samples.DialogHost.WithMultipleTextBoxes"
             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:local="clr-namespace:MaterialDesignThemes.UITests.Samples.DialogHost"
             xmlns:materialDesign="http://materialdesigninxaml.net/winfx/xaml/themes"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             d:DesignHeight="450"
             d:DesignWidth="800"
             mc:Ignorable="d">
  <materialDesign:DialogHost x:Name="SampleDialogHost" Loaded="DialogHost_Loaded">
    <materialDesign:DialogHost.DialogContent>
      <StackPanel Margin="16"
                  HorizontalAlignment="Center"
                  VerticalAlignment="Center">
        <TextBox x:Name="TextBoxOne"
                 MinWidth="200"
                 Text="One" />
        <TextBox x:Name="TextBoxTwo"
                 MinWidth="200"
                 Text="Two" />
        <TextBox x:Name="TextBoxThree"
                 MinWidth="200"
                 Text="Three" />
      </StackPanel>
    </materialDesign:DialogHost.DialogContent>
  </materialDesign:DialogHost>
</UserControl>