mystile top nav bacground color

Hi all,
I’m using Mystile theme with woocommerce.
I have simple problem, to change background color for top nav menu? where is cart, checkout, search…?
i tried in style.css for mystile in here:

/* 2.2.2 Top Navigation (optional) */
#top {
  background: #f7f7f7;
  margin: 0 -1.618em;
  padding: 1.618em;
}

but its not working.
Thanks!