x-sizing: border-box;
        }

        body {
            font-family: 'SF Pro Display', -apple-system, BlinkMacSystemFont, sans-serif;
            background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
            min-height: 100vh;
            color: #333;
        }

        .header {
            background: rgba(0, 0, 0, 0.1);
            backdrop-filter: blur(10px);
            padding: 1rem 2rem;
            border-bottom: 1px solid rgba(255, 255, 255, 0.1);
        }

        .header h1 {
  