How to change global font size and styles | 2017 theme

Hi,

I successfully added a style changes in the “Customizing Additional CSS” section of the 2017 theme e.g.:

.navigation-top a {
  color: #222;
  font-weight: 300;
	letter-spacing: 0.3em;
	font-size: .4 em;
  -webkit-transition: color 0.2s;
  transition: color 0.2s;
}

I’d like to add a style that overrides the global body text styles. I tried adding the code below, but it did not work. Is it possible to do so in the “Customizing Additional CSS” section?

p {
font-size: 12px;
}