W3.CSS is a modern framework with built-in responsiveness and easy to learn and use compared to other CSS frameworks. It aims to speed up and simplify web development and support modern responsive devices like Mobile, Laptop, Tablet and Desktop.More..
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<html>
<title>W3.CSS</title>
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="https://www.w3schools.com/w3css/4/w3.css">
<body class="w3-container w3-auto">
<h2>Display Warnings</h2>
<p>The w3-panel class can be used to display warnings:</p>
<div class="w3-panel w3-pale-yellow w3-border">
<h3>Warning!</h3>
<p>Yellow often indicates a warning that might need attention.</p>
</div>
<div class="w3-panel w3-yellow w3-border">
<h3>Warning!</h3>
<p>Yellow often indicates a warning that might need attention.</p>
</div>
</body>
</html>