section {
	display: flex;
	height: 120px;
}

section:nth-child(2) div {
	flex-grow: 1; /* All grow equally. */
}

section:nth-child(3) div:nth-child(1) {
	background-color: hotpink;
	flex-grow: 1; /* Just grow this one. */
}

section:nth-child(4) div:nth-child(1) {
	background-color: hotpink;
	flex-grow: 1;
}

section:nth-child(4) div:nth-child(2) {
	background-color: crimson;
	flex-grow: 2; /* Grow twice as much. */
}

section:nth-child(5) div {
	width: 50%; /* With 3 `div` would be 150%. */
}

section:nth-child(5) div:nth-child(1) {
	background-color: lightsalmon;
	flex-shrink: 0; /* Don’t shrink this one! */
}
body {
	font-family: sans-serif;
	padding: 20px;
}

div {
	background-color: tomato;
	border-bottom: 2px solid firebrick;
	border-right: 2px solid firebrick;
	padding: 5px;
}

section {
	background-color: gold;
}

section:not(:first-child) {
	margin-top: 20px;
}
<!DOCTYPE html>
<html>
	<head>
		<meta name="viewport" content="width=device-width, initial-scale=1">
		<link href="/assets/styles/reset.css" rel="stylesheet">
		<link href="setup.css" rel="stylesheet">
		<link href="style.css" rel="stylesheet">
	</head>
	<body>
		<section>
			<div>
				<p>Item 1</p>
			</div>
			<div>
				<p>Item 2</p>
			</div>
			<div>
				<p>Item 3</p>
			</div>
		</section>
		<section>
			<div>
				<p>Item 1</p>
			</div>
			<div>
				<p>Item 2</p>
			</div>
			<div>
				<p>Item 3</p>
			</div>
		</section>
		<section>
			<div>
				<p>Item 1</p>
			</div>
			<div>
				<p>Item 2</p>
			</div>
			<div>
				<p>Item 3</p>
			</div>
		</section>
		<section>
			<div>
				<p>Item 1</p>
			</div>
			<div>
				<p>Item 2</p>
			</div>
			<div>
				<p>Item 3</p>
			</div>
		</section>
		<section>
			<div>
				<p>Item 1</p>
			</div>
			<div>
				<p>Item 2</p>
			</div>
			<div>
				<p>Item 3</p>
			</div>
		</section>
	</body>
</html>