.grid-container {
  display: grid;
  grid-template-areas:
    'header header'
    'sidebar main'
    'footer footer';
  grid-gap: 10px;
}
.header {
  grid-area: header;
}
.sidebar {
  grid-area: sidebar;
}
.main {
  grid-area: main;
}
.footer {
  grid-area: footer;
}

.grid-item {
  padding: 20px;
  background-color: lightgrey;
}