Anyone know how to or if you are able to make all these transparent?
Why?
It looks a bit weird to have dark sides and topbar clear that is why I ask.
currently using a local script with
game.Players.LocalPlayer:WaitForChild(“PlayerGui”):SetTopbarTransparency(1)
game:GetService(“StarterGui”):SetCore("TopbarEnabled", false)
It removes definitely everything.
I think he meant changing the background transparency of the chat frame and the player list, not hiding them? 
We shall wait for his reply then…
Unfortunately, because the PlayerList is not a part of the main UI it is (probably) not alterable. However, the chat recently was updated to be completely open-sourced and editable for all games, so you can use a script to alter the chat frame itself or put a script in the “Chat” service to do it.
If you’re in play solo, you’re able to find the correct path of the frame you need to change.
Hopefully this helps. 
(since im bad at explaining pm me for more details)
Are you doing that as a LocalScript in StarterPlayer?
There is no way to modify the transparency of the core UI at the moment.
If you really need this feature, I would suggest making a feature request.
CORRECTION :
This might be of use.
Im not trying to do the text mainly the backgrounds so they all match and are clear unless it would just be more easer to disable them and code a special chat and leaderboard system.
The API I linked only fades out the background, not the text.
Sorry, Was a bit confused saying the title was " Lua Chat System /Client API/ChatWindow"
Yes, that should be in a LocalScript or a ModuleScript running on the client, and like @joritochip mentioned, There’s no possible way to change the PlayerList apart from hiding it using the void :SetCoreGuiEnabled, However, the chat like jorito mentioned, can be edited and can be accessed through game.Players.LocalPlayer:WaitForChild("PlayerGui").Chat, You can also find the gui when you run solo mode, Navigate to Players > LocalPlayer (YourPlayer) > PlayerGui and you should find a gui by the name of “Chat”, you can open it and see its contents, and in fact, you can edit the content’s properties as you wish.
For this example, I changed the BackgroundColor3 for some frames and now the chat looks fresh and stylish:
