W3Schools Tryit Editor

<!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/5/w3.css">
<body>

<div class="w3-container">
<h2>Circular buttons (w3-button)</h2>
<p>The <strong>w3-circle</strong> class creates a circular button.</p>
</div>

<div class="w3-container">
<p><button class="w3-button w3-circle w3-black">Button</button></p>
<p><button class="w3-button w3-circle w3-teal">Button</button></p>
<p><button class="w3-button w3-circle w3-red">Button</button></p>
<p><button class="w3-button w3-circle w3-black">1</button></p>
<p><button class="w3-button w3-circle w3-teal">2</button></p>
<p><button class="w3-button w3-circle w3-red">3</button></p>
</div>

<div class="w3-container w3-xlarge">
<p><button class="w3-button w3-circle w3-black">Button</button></p>
<p><button class="w3-button w3-circle w3-teal">Button</button></p>
<p><button class="w3-button w3-circle w3-red">Button</button></p>
<p><button class="w3-button w3-circle w3-black">1</button></p>
<p><button class="w3-button w3-circle w3-teal">2</button></p>
<p><button class="w3-button w3-circle w3-red">3</button></p>
</div>

</body>
</html>