<!DOCTYPE html>
<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>
<div class="w3-container">
<h2>Hoverable Borders</h2>
<div style="border:16px solid white" class="w3-panel w3-hover-border-green">
<p>Thick white (invisible) border that turns green on hover.</p>
</div>
<div style="border:16px solid white" class="w3-panel w3-hover-border-black">
<p>Thick white (invisible) border that turns black on hover.</p>
</div>
</div>
</body>
</html>