Edit in JSFiddle

Result
HTML
CSS

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8" />
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <title>Grid</title>
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link rel="stylesheet" type="text/css" media="screen" href="./main.css" />
</head>
<body>
  <div class="container">
    <header></header>
    <section class="sidebar"></section>
    <main></main>
    <footer></footer>
  </div>
</body>
</html>

html,
body {
  margin: 0;
  padding: 0;
  height: 100%;
}

.container {
  display: grid;
  height: 100%;
  grid-template-columns: repeat(2, 40px 20%);
  grid-template-rows: repeat(4, 25%);
  grid-row-gap: 10px;
  grid-column-gap: 10px;
}

header,
footer,
.sidebar,
main {
  box-sizing: border-box;
}

header {
  grid-area: 1 / 1 / span 1 / span 8;
  background: #ddd;
}

footer {
  grid-row: 4 / 5;
  grid-column: 1 / 9;
  background: #aaa;
}

.sidebar {
  grid-row-start: 2;
  grid-row-end: span 2;
  grid-column-start: 1;
  grid-column-end: 3;
  background: #888;
}

main {
  grid-area: 2 / 3 / 4 / 9;
  background: #ccc;
}