I think you have supplied 4 different codes now.
I just pasted them into an editor to compare but im seeing differances.
Can you place the actual code one more time? One of your examples is missing a semicolon ; i think but im not sure if it supposed to be there or not.
Also the other code starts with a line of "@media (max-width: 768px){"
but you didnt place it in your reply so now im confused as to what you want to be correct