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

using System;

namespace Spectre.Console.Rendering
{
    /// <summary>
    /// Represents a border with a heavy edge.
    /// </summary>
    public sealed class HeavyEdgeBorder : Border
    {
        /// <inheritdoc/>
        public override Border? SafeBorder => Border.Square;

        /// <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."),
            };
        }
    }
}