feat(debug): render debug support

src/element.zig

@@ -52,8 +52,17 @@ pub fn Element(Event: type) type {
         ///   Otherwise user specific errors should be caught using the `handle`
         ///   function before the rendering of the `Container` happens.
         pub inline fn content(this: @This(), cells: []Cell, size: Point) !void {
-            if (this.vtable.content) |content_fn|
+            if (this.vtable.content) |content_fn| {
                 try content_fn(this.ptr, cells, size);
+
+                // DEBUG render corresponding top left corner of this `Element` *red*
+                // - only rendered if the corresponding associated element renders contents into the `Container`
+                if (comptime build_options.debug) {
+                    cells[0].style.fg = .red;
+                    cells[0].style.bg = .black;
+                    cells[0].cp = 'e'; // 'e' for *element*
+                }
+            }
         }
     };
 }
@@ -260,6 +269,7 @@ pub fn Scrollable(Event: type) type {
 
 const std = @import("std");
 const assert = std.debug.assert;
+const build_options = @import("build_options");
 const input = @import("input.zig");
 const Container = @import("container.zig").Container;
 const Cell = @import("cell.zig");