<div class="wrapper">
  <div>1</div>
  <div>2</div>
  <div>3</div>
  <div>4</div>
  <div>5</div>
  <div>6</div>
  <div>7</div>
  <div>8</div>
  <div>9</div>
</div>

document, body {
   background: #ccc;
   margin: 0px;
   height: 100%;
}
.wrapper {
   display: grid;
   grid-template-columns: 1fr 1fr 1fr;
   grid-template-rows:  1fr 1fr 1fr;
   min-height: 100vh;
}

.wrapper div {
   background: #FFF;
   margin: 2px;
   padding: 5px;
}