grid-template-areas

HTML

<body>
    <nav>Navigation</nav>
    <header>Header</header>
    <section>Sidebar</section>
    <main>Main Content</main>
    <aside>Aside 1</aside>
    <aside>Aside 2</aside>
    <aside>Aside 3</aside>
    <footer>Footer</footer>          
</body>

CSS

body {
  width: 100vw;
  height: 100vh;

  display: grid;
  grid-template-areas:
    "nav nav nav"
    "head head head"
    "sidebar content content"
    "aside1 aside2 aside3"
    "footer footer footer";

  // Sizing
  grid-template-rows: 50px 200px 1fr 250px 50px;
  grid-template-columns: repeat(3, 1fr);
}
    
#nav {
  grid-area: nav;
}
#header {
  grid-area: head;
}
#sidebar {
  grid-area: sidebar;
}
#main {
  grid-area: content;
}
#aside1 {
  grid-area: aside1;
}
#aside2 {
  grid-area: aside2;
}
#aside3 {
  grid-area: aside3;
}
#footer {
  grid-area: footer;
}

Main Content