Popup with controls

[Amakesh]

I would like the

AddCustomMenuItem(
    "Change Label Color",
    function()
        local color = nil

        color = unpack(self.labelSettings.labelColor)

        COLOR_PICKER:Show(
            function(...)
                self:SetLabelColor(...)
            end,
            color
        )
    end
)

method to show me a popup with two dropdowns and one slider instead of the colorpicker. Unfortunately, no matter which way I try, I always get just a popup with title, maintext and cancel and ok buttons.
What can I do to get the aforementioned controls in the window as well?
I tried both ZO_Dialogs(see example below) and libDialog.

	ZO_Dialogs_RegisterCustomDialog("ExampleDialog", {

		setup = function(dialog)
			d("Setting up dialog controls")
	
			local parentControl = dialog.control
			local slider = CreateControlFromVirtual("$(parent)Slider", parentControl, "ZO_Slider")
	
			if slider then
				slider:SetAnchor(TOPLEFT, parentControl, TOPLEFT, 0, 20)
				slider:SetMinMax(0, 100)
				slider:SetValue(50)
				slider:SetValueStep(1)
				slider:SetHandler("OnValueChanged", function(_, value)
					d("Slider value: " .. value)
				end)
				
				dialog.slider = slider
			else
				d("Failed to create slider.")
			end
		end,

		title = {
			text = "Example Dialog",
		},
		mainText = {
			text = "Adjust the slider:",
		},
	
		buttons = {
			{
				text = "OK",
				callback = function(dialog)
					d("Confirmed with slider value: " .. dialog.slider:GetValue())
				end,
			},
			{
				text = "Cancel",
				callback = function(dialog)
					d("Dialog cancelled")
				end,
			},
		},
	})
	

SLASH_COMMANDS["/showdialog"] = function()
    ZO_Dialogs_ShowDialog("ExampleDialog")
end