Edit in JSFiddle

<header class="main-header">Header</header>
<main class="content">Main content goes here</main>
<aside class="primary-sidebar">Sidebar (left)</aside>
<aside class="secondary-sidebar">Sidebar (right)</aside>
<footer class="main-footer">Footer</footer>

* {
  padding: 0;
  margin: 0;
}

body {
  font-size: 1.2em;
  text-align: center;
  
  height: 100vh;
  display: grid;
  grid-template-columns: 20% 1fr 20%;
  grid-template-rows: auto 1fr auto;
  grid-template-areas:
    "header      header  header"
    "sidebar-pri content sidebar-alt"
    "footer      footer  footer";
}

.main-header {
  background: red;
  grid-area: header;
}

.main-footer {
  background: red;
  grid-area: footer;
}

.primary-sidebar, .secondary-sidebar {
  background: turquoise;
}

.primary-sidebar {
  grid-area: sidebar-pri;
}

.secondary-sidebar {
  grid-area: sidebar-alt;
}

.content {
  background: green;
  grid-area: content;
}