There is nothing wrong with your code. The following works just fine on my system (Safari on macOS), which has Optima installed but not Century Gothic.

body {
  font-family: Optima, 'Century Gothic', sans-serif;
}

Lorem ipsum dolor sit amet.

Which browser and operating system are you using? Is your website available on the internet? If so, can you provide a link to it? Or are you just opening the local files in your browser?