What does it mean?
Really got that look nailed down.
Nailed down is a phrase similar to nailed it.
From this site
"Nailed It is a phrase used to express success after achieving something seemingly difficult with relative ease. Online, it is often found as a caption on image macros or in sarcastic commentary criticizing the quality of success, especially in response to attempts at recreating recipes or craft projects."
The site also lists the origin, spread and a few notable examples.
Also, the urban dictionary includes a similar definition.