https://learn.microsoft.com/en-us/windows/windows-app-sdk/api/winrt/microsoft.ui.xaml.controls.control.borderbrush?view=windows-app-sdk-2.0
Control.BorderBrush Property (Microsoft.UI.Xaml.Controls) - Windows App SDK | Microsoft Learn
Gets or sets a brush that describes the border fill of a control.
windows appcontrolpropertymicrosoftui