On top of sth. 完全控制，做得好
Do you think he's really on top of his job?
A: How is the new project going?
B: Don’t worry. I was on top of it while you were on vacation.
On top of it/that
We missed our flight, and on top of that we had to wait seven hours for the next one.
top n. 上衣
I need a top to go with these trousers.
From top to bottom 彻底
She searched the apartment from top to bottom for the missing letters.
On top of the world 极度开心
I’m on top of the world; I’ve just had a baby son.