<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=0">
<style>
* {margin: 0;padding: 0;}
html,body {width: 100%;height: 100%;}
.container {
display: grid;
grid-template-columns: 33.333333% 33.333333% 33.333333%;
grid-template-rows: auto;
}
.item {
background-color: #444;
color: #fff;
font-size: 150%;
padding: 20px;
margin: 3.333333%;
}
.item-5 {
grid-column-start: 2;
grid-column-end: 4;
grid-row-start: 2;
grid-row-end: 4;
}
.item-7 {
grid-column-start: 1;
grid-column-end: 3;
grid-row-start: 4;
grid-row-end: 4;
}
.item-12 {
grid-column-start: 1;
grid-column-end: 4;
grid-row-start: 6;
grid-row-end: 6;
}
</style>
</head>
<body>
<div class="container">
<div class="item item-1">1</div>
<div class="item item-2">2</div>
<div class="item item-3">3</div>
<div class="item item-4">4</div>
<div class="item item-5">5</div>
<div class="item item-6">6</div>
<div class="item item-7">7</div>
<div class="item item-8">8</div>
<div class="item item-9">9</div>
<div class="item item-10">10</div>
<div class="item item-11">11</div>
<div class="item item-12">12</div>
</div>
</body>
</html>