What difference between "you're working hard today" and "you've worked hard today"? I think these sentences have the same meaning, but I'm not sure.
You are working hard today --> you're still doing the work.
Example: You are a boss in an office and you're finding one of your staff exhausted while he/she is STILL WORKING. Then you say "You can take some rest, you're working hard today."
You have worked hard today. --> you have finished the work.
Example: You are a boss in an office and accidentally meet one of your staff in a restaurant while you're having dinner. You may say "Hello John, thanks for you papers. You have worked hard today."