Sizing

Sizing.Size

The inherited Size attached property (xs / sm / md / lg) scales height, font size and padding. Since it inherits, setting it on a panel sizes every child.

<!-- Attached property drives height, font size and padding -->
<Button toolkit:Sizing.Size="xs" />
<Button toolkit:Sizing.Size="sm" />
<Button toolkit:Sizing.Size="md" />  <!-- default -->
<Button toolkit:Sizing.Size="lg" />

<!-- Size is inherited, so a panel sets it for every child -->
<StackPanel toolkit:Sizing.Size="lg">
    <TextBox /> <ComboBox /> <Button>OK</Button>
</StackPanel>

Other controls honor the same attached property — TreeView scales its expander, indentation and text together:

<TreeView toolkit:Sizing.Size="lg" ItemsSource="{Binding Tree}" />

Sizing.IsSquare

IsSquare forces equal width and height, for single-icon buttons.

<Button toolkit:Sizing.IsSquare="True"
        toolkit:Sizing.Size="lg">
    <fonts:FontIcon Text="{x:Static fonts:LucideFontIcons.Leaf}" />
</Button>