Adding New Style

With dotnet cli

dotnet new avalonia.styles -o Styles -n NewStyle

Default Template

Style template ships with a portion for previewer where you can add testing controls to see whether those styles works properly.

<Styles xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
  <Design.PreviewWith>
    <Border Padding="20">
      <!-- Add Controls for Previewer Here -->
    </Border>
  </Design.PreviewWith>

  <!-- Add Styles Here -->
</Styles>

Define a Style

A style starts with a Selector which is the rule of target matching, for figuring out which control should have those contained styling. Contained styling is some key-value pair on properties.

<Styles xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
  <Design.PreviewWith>
    <Border Padding="20">
      <!-- Add Controls for Previewer Here -->
    </Border>
  </Design.PreviewWith>

  <!-- Add Styles Here -->
  <Style Selector="TextBlock.h1">
    <Setter Property="FontWeight" Value="Bold" />
    <Setter Property="FontSize" Value="15" />
    <Setter Property="Margin" Value="5" />
  </Style>

</Styles>