W3.CSS Containers
W3.CSS provides two classes w3-container, w3-panel that are used mostly with container elements (like <div>, <header>, <footer>, <article>, <section> etc) of HTML for providing common padding and margin to the elements.
w3-container : The w3-container class is used to add 16px left and right padding to HTML elements.
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="https://www.w3schools.com/w3css/4/w3.css">
</head>
<body>
<div class="w3-container w3-yellow">
<h1> ABC</h1>
<p> I am Container 1 </p>
</div>
<div class="w3-container w3-red">
<h1> DEF</h1>
<p> I am Container 2 </p>
</div>
</body>
</html>