If you take advantage of width: 100vw; and height: 100vh;, the object with these styles applied will stretch to the full width and height of the device.
Also note, there are times padding and margins can get added to your view, by browsers and the like. I added a * global no padding and margins so you can see the difference. Keep this in mind.
*{
box-sizing: border-box;
padding: 0;
margin: 0;
}
.wrapper {
display: grid;
border-style: solid;
border-color: red;
grid-template-columns: repeat(3, 1fr);
grid-template-rows: repeat(3, 1fr);
grid-gap: 10px;
width: 100vw;
height: 100vh;
}
.one {
border-style: solid;
border-color: blue;
grid-column: 1 / 3;
grid-row: 1;
}
.two {
border-style: solid;
border-color: yellow;
grid-column: 2 / 4;
grid-row: 1 / 3;
}
.three {
border-style: solid;
border-color: violet;
grid-row: 2 / 5;
grid-column: 1;
}
.four {
border-style: solid;
border-color: aqua;
grid-column: 3;
grid-row: 3;
}
.five {
border-style: solid;
border-color: green;
grid-column: 2;
grid-row: 4;
}
.six {
border-style: solid;
border-color: purple;
grid-column: 3;
grid-row: 4;
}<html>
<div class="wrapper">
<div class="one">One</div>
<div class="two">Two</div>
<div class="three">Three</div>
<div class="four">Four</div>
<div class="five">Five</div>
<div class="six">Six</div>
</div>
</html>