how do you identify a grid area in css code example

Example 1: grid-template-areas css

#page {
  display: grid;
  width: 100%;
  height: 250px;
  grid-template-areas: "head head"
                       "nav  main"
                       "nav  foot";
  grid-template-rows: 50px 1fr 30px;
  grid-template-columns: 150px 1fr;
}

#page > header {
  grid-area: head;
  background-color: #8ca0ff;
}

#page > nav {
  grid-area: nav;
  background-color: #ffa08c;
}

#page > main {
  grid-area: main;
  background-color: #ffff64;
}

#page > footer {
  grid-area: foot;
  background-color: #8cffa0;
}

Example 2: how to use a blank space with grid template areas css

.container {
  display: grid;

  grid-template-columns: 2fr 2fr 1fr 2fr;
  grid-template-rows: 100px 200px 100px;

  grid-template-areas:
    "head head . side"
    "main main . side"
    "footer footer footer footer";
}