HTML/CSS - LUNH ALGO (EXPLAINED) Online Editor and JavaScript Compiler

html
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Luhn Algorithm Explained</title>
    <link href="https://fonts.googleapis.com/css2?family=Roboto:wght@300;400;700&family=Playfair+Display:wght@700&family=Source+Code+Pro&display=swap" rel="stylesheet">
    <style>
        body {
            font-family: 'Roboto', sans-serif;
            line-height: 1.6;
            max-width: 800px;
            margin: 0 auto;
            padding: 20px;
            background-color: #f5f5f5;
        }
        .container {
            background: white;
            padding: 30px;
            border-radius: 10px;
            box-shadow: 0 0 20px rgba(0,0,0,0.1);
        }
        h1 {
            font-family: 'Playfair Display', serif;
            font-size: 2.5em;
            color: #2c3e50;
css
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