body { 
            display: flex; justify-content: center; align-items: center; 
            height: 100vh; background: #eceff1; margin: 0; 
        }
        canvas { 
            background: white; padding: 15px; border-radius: 5px;
            box-shadow: 0 4px 15px rgba(0,0,0,0.1); 
        }