<header>
  Header Section
</header>
<aside>
  Aside Section
</aside>
<main>
  Main Section
</main>
<footer>
  Footer Section
</footer>
@import url("https://fonts.googleapis.com/css2?family=Exo:wght@600&display=swap");

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

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

  font-family: "Exo", Arial, sans-serif;
  background-color: #f7f7f7;
}

body {
  display: grid;
  gap: 10px;
  grid-template-rows: min-content auto min-content;
  grid-template-columns: repeat(12, 1fr);
  grid-template-areas:
    "header header header header header"
    "aside aside main main main"
    "footer footer footer footer footer";
}

body > * {
  color: #fff;
  display: flex;
  justify-content: center;
  align-items: center;
}

header {
  grid-column: header-start / header-end;
  background-color: #040f17;
  min-height: 88px;
}

aside {
  grid-column: aside-start / header-end;
  background-color: #09f;
}

main {
  grid-column: header-end / -1;
  background-color: #ff5722;
}

footer {
  grid-column: aside-end / -1;
  background-color: #3f51b5;
  min-height: 100px;
}

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

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