Formal:
* आप बहुत खूबसूरत लग रहे हैं। (Aap bahut khubsurat lag rahe hain.) - "You are looking very beautiful."
* आप बहुत सुंदर दिख रहे हैं। (Aap bahut sundar dikh rahe hain.) - "You are looking very beautiful."
* आप अद्भुत लग रहे हैं। (Aap adbhut lag rahe hain.) - "You look amazing."
Informal:
* तुम बहुत खूबसूरत लग रही हो। (Tum bahut khubsurat lag rahi ho.) - "You look very beautiful." (For a woman)
* तुम बहुत सुंदर दिख रहे हो। (Tum bahut sundar dikh rahe ho.) - "You look very handsome." (For a man)
* तुम कमाल लग रहे हो। (Tum kamaal lag rahe ho.) - "You look awesome."
More expressive:
* तुम बहुत ही खूबसूरत लग रही हो। (Tum bahut hi khubsurat lag rahi ho.) - "You look absolutely stunning."
* तुम बहुत ही आकर्षक लग रहे हो। (Tum bahut hi aakarshak lag rahe ho.) - "You look very attractive."
Important Notes:
* The use of "आप" (aap) is more formal than "तुम" (tum).
* "लग रहे हैं" (lag rahe hain) is used for men, and "लग रही हो" (lag rahi ho) is used for women.
* You can use "आप" for both men and women in a formal setting.
Remember that the best way to say "you look stunning" in Hindi depends on the specific situation and your relationship with the person you are talking to.