header {
  width: 90vw;
  margin: auto;
  display: grid;
  grid-template-columns: 22.5vw 45vw 22.5vw;
  column-rule: 1px solid black;
}
header > :not(header) {
  margin: 0 1rem;
}

nav ul {
  list-style: none;
  text-align: center;
  padding: 0;
}
nav li {
  display: inline;
}

#content {
  width: 90vw;
  margin: auto;
  display: grid;
  grid-template-columns: 22.5vw 45vw 22.5vw;
  column-rule: 1px solid black;
}
#content > :not(header) {
  margin: 0 1rem;
}

header {
  grid-column: span 3;
}

#left {
  order: 1;
}

main {
  order: 2;
}

#right {
  order: 3;
}

h1, #left h2, #right h2 {
  text-align: center;
}

article h1 {
  text-align: left;
}