spectre.console/src/Spectre.Console/Rendering/Borders/MinimalDoubleHeadBorder.cs

using System;

namespace Spectre.Console.Rendering
{
    /// <summary>
    /// Represents a minimal border with a double header border.
    /// </summary>
    public sealed class MinimalDoubleHeadBorder : Border
    {
        /// <inheritdoc/>
        protected override string GetBoxPart(BorderPart part)
        {
            return part switch
            {
                BorderPart.HeaderTopLeft => " ",
                BorderPart.HeaderTop => " ",
                BorderPart.HeaderTopSeparator => " ",
                BorderPart.HeaderTopRight => " ",
                BorderPart.HeaderLeft => " ",
                BorderPart.HeaderSeparator => "│",
                BorderPart.HeaderRight => " ",
                BorderPart.HeaderBottomLeft => " ",
                BorderPart.HeaderBottom => "═",
                BorderPart.HeaderBottomSeparator => "╪",
                BorderPart.HeaderBottomRight => " ",
                BorderPart.CellLeft => " ",
                BorderPart.CellSeparator => "│",
                BorderPart.CellRight => " ",
                BorderPart.FooterBottomLeft => " ",
                BorderPart.FooterBottom => " ",
                BorderPart.FooterBottomSeparator => " ",
                BorderPart.FooterBottomRight => " ",
                _ => throw new InvalidOperationException("Unknown box part."),
            };
        }
    }
}