nail down (someone or something)
to make certain or sure of something
I am trying to nail down the exact time that the meeting will begin.
Amazing beauty Secrets
Know Your Shade
When choosing a foundation, test a product on the skin near your jawline. And be sure to do it in natural light. This will ensure the foundation tone you choose for your face isn t too different from the natural shade of your neck. We really love Makeup Forever s Invisible Cover HD Foundation because it comes in so many shades.