Avalonia/samples/ControlCatalog/MainView.xaml

<UserControl x:Class="ControlCatalog.MainView"
             xmlns="https://github.com/avaloniaui"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:controls="clr-namespace:ControlSamples;assembly=ControlSamples"
             xmlns:pages="clr-namespace:ControlCatalog.Pages"
             xmlns:models="clr-namespace:ControlCatalog.Models">
  <Grid>
    <Grid.Styles>
      <Style Selector=":min-width(600) TextBlock#MinWidth">
        <Setter Property="Foreground" Value="Red" />
      </Style>
      <Style Selector=":max-width(800) TextBlock#MaxWidth">
        <Setter Property="Foreground" Value="Red" />
      </Style>
      <Style Selector=":min-height(600) TextBlock#MinHeight">
        <Setter Property="Foreground" Value="Red" />
      </Style>
      <Style Selector=":max-height(800) TextBlock#MaxHeight">
        <Setter Property="Foreground" Value="Red" />
      </Style>
    </Grid.Styles>
    <StackPanel Spacing="10">
      <TextBlock Name="MinWidth" Classes="h2" Text="min-width" />
      <TextBlock Name="MaxWidth" Classes="h2" Text="max-width" />
      <TextBlock Name="MinHeight" Classes="h2" Text="min-height" />
      <TextBlock Name="MaxHeight" Classes="h2" Text="max-height" />
    </StackPanel>
  </Grid>
</UserControl>