:root{--primary: #3b82f6;--primary-dark: #1e40af;--accent: #f59e0b;--success: #10b981;--danger: #ef4444;--bg-light: #f9fafb;--bg-white: #ffffff;--text-dark: #1f2937;--text-light: #6b7280;--border: #e5e7eb;--shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, .05);--shadow-md: 0 4px 6px -1px rgba(0, 0, 0, .1);--shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, .1)}*{margin:0;padding:0;box-sizing:border-box}body{font-family:-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,Oxygen,Ubuntu,Cantarell,Fira Sans,Droid Sans,Helvetica Neue,sans-serif;-webkit-font-smoothing:antialiased;-moz-osx-font-smoothing:grayscale;background-color:var(--bg-light);color:var(--text-dark)}.lesson-viewer{max-width:900px;margin:0 auto;background:var(--bg-white);border-radius:12px;overflow:hidden;box-shadow:var(--shadow-lg)}.lesson-header{padding:32px;background:linear-gradient(135deg,var(--primary) 0%,var(--primary-dark) 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