How would I make a gui in front of the starter roblox guis like Leaderboard and Tools and Chat?

I'm trying to make a gui that needs to go in front of the chat gui because the chat gui is messing up the look of it and the leaerboard gui and tools are overlapping it as well, I tried changing the Zindex but it didnt do anything

Try turning off ROBLOX Core GUI's http://wiki.roblox.com/index.php?title=Disabling_parts_of_the_game_interface LINK^^^^