Live Demo: Example of Controlling the Dimensions of Flex Items

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Example of Controlling the Dimensions of Flex Items</title>
<style>
.flex-container {
    width: 80%;
    min-height: 300px;
    margin: 0 auto;
	font-size: 32px;
    display: -webkit-flex; /* Safari */     
    display: flex; /* Standard syntax */
    border: 1px solid #666;
}
.flex-container div {
	padding: 10px;
}
.item1 {
	background: #e84d51;
	-webkit-flex: 1; /* Safari */
    flex: 1; /* Standard syntax */
}
.item2 {
	background: #7ed636;
	-webkit-flex: 2; /* Safari */
    flex: 2; /* Standard syntax */
}
.item3 {
	background: #2f97ff;
	-webkit-flex: 1; /* Safari */
    flex: 1; /* Standard syntax */
}
</style>
</head>
<body>
    <div class="flex-container">
        <div class="item1">Item 1</div>
        <div class="item2">Item 2</div>
        <div class="item3">Item 3</div>
    </div>
    <p><strong>Note:</strong> Experiment with the value of flex property for individual flex item to understand how the dimension of flex items are calculated.</p>
</body>
</html>