Making a skybox in Unity

Beginning the process of replicating the concept art below into Unity

My scene in Unity was missing the skybox - realised that the scene panel must have a button setting, similar to Maya. I think I'd inadvertently turned it off when using the asset store, during the creating a game in Oculus Quest tutorial.

Left - scene showing the skybox

Right - my scene with no skybox visible

I found out, through viewing a forum, that the skybox visibility button was turned off. 

Imported new skyboxes, via the asset store, to see if a midnight sky might work, using the link below.

The skybox settings are too light - even using a midnight sky. I don't want sky, stars or much light penetration. Therefore, I am going to custom make a skybox in photoshop, by creating a new material and applying it to a shader. Assets tab>create material>shader>(drop down option) Skybox6sided 

Researched how to make a custom skybox in photoshop

https://docs.unity3d.com/560/Documentation/Manual/HOWTO-UseSkybox.html  and found the link below.