<div class="wrapper">
	<div class="grid">
		<div class="item"></div>
		<div class="item"></div>
		<div class="item"></div>
		<div class="item"></div>
		<div class="item"></div>
		<div class="item"></div>
		<div class="item"></div>
		<div class="item"></div>
		<div class="item"></div>
		<div class="item"></div>
	</div>
</div>
* {
	box-sizing: border-box;
}

body {
	background-color: #212121;
}

.wrapper {
	max-width: 1200px;
	margin: 40px auto;
}

.grid {
	display: flex;
	flex-wrap: wrap;
	counter-reset: item;
	margin: -10px;
	width: calc(100% + 20px);
}

.item {
	width: calc((100% / 3) - 20px);
	margin: 0 10px 20px 10px;
	background-color: darkOrchid;
	border: 2px solid darken(darkOrchid, 10%);
	border-radius: 0.25em;
	counter-increment: item;
	padding: 20px;
	
	&::after {
		content: counter(item);
	}
}

External CSS

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External JavaScript

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