CSS Flexbox

Flexbox is a layout model that makes it easy to align and distribute elements within a container.

Example: 

<!DOCTYPE html>
<html>
<head>
    <style>
        .container {
            display: flex;
            justify-content: center;
            align-items: center;
            height: 100vh;
            background-color: lightgray;
        }
        .box {
            width: 100px;
            height: 100px;
            background-color: blue;
            color: white;
            text-align: center;
            line-height: 100px;
        }
    </style>
</head>
<body>
    <div class="container">
        <div class="box">Flex</div>
    </div>
</body>
</html>