Code style

Which code sample follows the CSS Code styles mentioned in the theory?

A)

.menu {
  margin: 0 1em 2em 0px;
  padding-top: 10px;
  padding-bottom: 20px;
}

B)

.yaaay {
  padding: 2em;
  color: #fff;
}

C)

.add-to-cart {
  background: #ddf;
  border: 1px solid orange;
  margin: 1em;  
}

D)

.nav {
  color: #ffbbcc;
  text-align: center;
  border: 1px solid black;
}