https://mozilladevelopers.github.io/playground/07-basic-layout

.container {
display: grid;
width: 750px;
height: 600px;
grid-template-columns: 200px 1fr 1fr;
grid-template-rows: 80px 1fr 1fr 100px;
grid-gap: 1rem;
}

.header {
grid-row: 1 / 2;
grid-column: 1 / 4;
}

.sidebar {
grid-row: 2 / 4;
grid-column: 1 / 2;
}

.content-1 {
grid-row: 2 / 3;
grid-column: 2 / 4;
}

.content-2 {
grid-row: 3 / 4;
grid-column: 2 / 3;
}

.content-3 {
grid-row: 3 / 4;
grid-column: 3 / 4;
}

.footer {
grid-row: 4 / 5;
grid-column: 1 / 4;
}

<div class=”container”>
<div class=”header”>header</div>
<div class=”sidebar”>sidebar</div>
<div class=”content-1″>Content-1</div>
<div class=”content-2″>Content-2</div>
<div class=”content-3″>Content-3</div>
<div class=”footer”>footer</div>
</div>