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<style>
#parent {
display: grid;
grid-template-columns: 100%;
grid-gap: 20px;
padding: 20px;
background: blue;
}
.child {
text-align: center;
padding: 20px;
font-size: 30px;
color: white;
}
#child-1 {
background: red;
}
#child-2 {
background: green;
}
#child-3 {
background: yellow;
}
</style>
<div id = "parent">
<div id = "child-1" class = "child">
<p>1</p>
</div>
<div id = "child-2" class = "child">
<p>2</p>
</div>
<div id = "child-3" class = "child">
<p>3</p>
</div>
</div>