Untitled

<!DOCTYPE html>
<html lang="en">
<head>
    <title>Practice</title>
    <link rel="stylesheet" href="practice.css">
</head>
<body>
    <div class="container">
    <div class="item">Item</div>
</div>
</body>
</html>

* {
    margin: 0;
    padding: 0;
}

.container {
    background-color: lightgray;
    display: flex;
    height: 300px;
    }

.item {
    width: 100px;
    height: 100px;
    margin: auto;

  }