A custom title that is better than Unity's

SimpleTitleAttribute.cs

using UnityEngine;

namespace SLController.Attributes {
	public class SimpleTitleAttribute: PropertyAttribute {
		public readonly string Text;
		public readonly string Style;

		public SimpleTitleAttribute(string text, string style = null) {
			Text = text;
			Style = style;
		}
	}
}

SimpleTitleAttributeDrawer.cs

using System.Linq;
using SLController.Attributes;
using UnityEditor;
using UnityEngine;

namespace SLController.Editor {
	[CustomPropertyDrawer(typeof(SimpleTitleAttribute))]
	public class SimpleTitleAttributeDrawer: DecoratorDrawer {
		private const float HEIGHT = 12;

		public override float GetHeight() {
			SimpleTitleAttribute title = attribute as SimpleTitleAttribute;
			GUIStyle style = title.Style ?? EditorStyles.boldLabel;
			
			float fullTextHeight = style.CalcHeight(new GUIContent(title.Text), 1.0f);
			int lines = 1;
			if (title.Text != null) {
				lines = title.Text.Count(a => a == '\n') + 1;
			}
			float eachLineHeight = fullTextHeight / lines;
			return EditorGUIUtility.singleLineHeight * 1.5f + eachLineHeight * (lines - 1);
		}

		public override void OnGUI(Rect position) {
			Rect titleRect = position;

			SimpleTitleAttribute title = attribute as SimpleTitleAttribute;
			EditorGUI.LabelField(titleRect, new GUIContent(title.Text), title.Style ?? EditorStyles.boldLabel);
			
			float indent = EditorGUI.indentLevel * 16;
			titleRect.height = 1;
			titleRect.x += indent;
			titleRect.width -= indent;
			titleRect.y += HEIGHT + 10;
			EditorGUI.DrawRect(titleRect, Color.gray);
		}
	}
}

[SimpleTitle("Systems")]
[SerializeField] private SerializedSystems _updateLoopSystems;