tested version with most of the final functionality. Still a few known issues, like dragging to a row that extends to multiple lines

RowCreateMarginContainer.cs

@@ -0,0 +1,32 @@
+using Godot;
+using System;
+
+public partial class RowCreateMarginContainer : MarginContainer
+{
+	[Export]
+	public Color DefaultColor = new(0, 0, 0, 1);
+	public readonly string Title = "Row";
+	// Called when the node enters the scene tree for the first time.
+	public override void _Ready()
+	{
+		(GetParent() as TabContainer).SetTabTitle(GetIndex(), Title);
+		ClearMenu();
+	}
+
+	// Called every frame. 'delta' is the elapsed time since the previous frame.
+	public override void _Process(double delta)
+	{
+	}
+	public void SendRowToGame()
+	{
+		var r = row.MakeRow(GetTree());
+		r.RowColor = GetNode<ColorPickerButton>("%RowCreateColorPickerButton").Color;
+		r.RowText = GetNode<TextEdit>("%RowTextEdit").Text;
+		this.GetParentOfType<game>().CallDeferred("AddRow", r, -1);
+	}
+	public void ClearMenu()
+	{
+		GetNode<ColorPickerButton>("%RowCreateColorPickerButton").Color = DefaultColor;
+		GetNode<TextEdit>("%RowTextEdit").Text = "";
+	}
+}