ColorPicker popup has no border or shadow

[ClarkThyLord]

Godot version

Godot 4.0 beta 3

System information

Windows 10

Issue description

Recent changes have removed border and shadow from ColorPicker popup seen in-engine with the default theme. Without these it's hard to tell where the ColorPicker popup starts and ends, nor is it in line with the overall default theme as other popups do have border and shadow.

For example, if ColorPicker popup is opened on top of a Panel control, it become almost impossible to know where the ColorPicker popup ends and the Panel starts; as seen below:

Ideally ColorPicker popup should look as follows:

Steps to reproduce

1. Open Godot engine with default theme
2. Press on any ColorPickerButton in-engine

Minimal reproduction project

N/A