Border draws a border around a single content visual.
new Border(new TextArea("TextArea inside a Border"));
You can override the border glyphs and border colors on a per-border basis using BorderStyle:
using XenoAtom.Terminal.UI.Styling;
new Border("Rounded").Style(BorderStyle.Rounded);
Use the factory constructor to dynamically recompute content:
new Border(() => new TextBlock(DateTime.Now.ToString("T")));
Border is a layout container: the border consumes space around its content.Group.HorizontalAlignment = Align.Start, VerticalAlignment = Align.Start