As Matt says, in British English we use the present perfect (You've made) for something which the other person has just done. You are delighted now, and you're thanking the person now. British English speakers would use the past (You made) if the person did the kind thing (or you received the present, for example) at some time in the past, such as yesterday or last week. American English speakers, as Christine says, would probably use the past form (You made) in both cases. This is a key difference between the grammar systems of GB and US English.

4 - The police are ________an investigation into the robbery

"You have made my day" is grammatically correct BUT "you made my day" is the commonly used phrase. It's a casual term that usually implies "you made my day better"; i.e., "Thanks for the card -- you really made my day!"

"You have made my day" is for now. "You made my day" is in the past, so either earlier today or before. ===== Examples: "Thanks so much for the wonderful present. (You have / It has) made my day." "Thanks so much for the wonderful present. I opened it (this morning / yesterday). (You / It) made my day."