Unity tip: Work with your canvas in Camera space, switch to Overlay on Play.

CanvasRenderModeSwitcher.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

// Unity tip"
// Usually it is desired that the HUD canvas is separated from Camera effects, or "ScreenSpaceOverlay" mode
// But Overlay canvases are terrible to work with
// So keep your canvas in "Screen Space Camera", and switch it automatically to Overlay when the game starts

public class CanvasRenderModeSwitcher : MonoBehaviour
{
	public RenderMode newRenderMode = RenderMode.ScreenSpaceOverlay;

	void Start ()
	{
		Canvas canvas = GetComponent<Canvas>();
		if (canvas != null)
			canvas.renderMode = newRenderMode;
	}
}