:root {
            --chem-primary: #4A90E2; 
            --chem-ink: #0f172a; 
            --chem-line: #dbeafe; 
            --chem-soft: #eff6ff; 
            --chem-warm: #fff7ed; 
        }

        .chemistry-hero { background: linear-gradient(135deg, #eff6ff 0%, #ffffff 52%, #fff7ed 100%); border: 1px solid var(--chem-line); border-radius: 12px; padding: clamp(20px, 4vw, 36px); margin-bottom: 24px; }
        .chemistry-hero .eyebrow { color: var(--chem-primary); font-weight: 800; text-transform: uppercase; font-size: 0.82rem; }
        .chemistry-hero h1 { color: var(--chem-ink); line-height: 1.14; margin: 10px 0 12px; }
        .chemistry-hero p { color: #475569; line-height: 1.75; max-width: 820px; }

        .chemistry-facts { display: grid; grid-template-columns: repeat(auto-fit, minmax(170px, 1fr)); gap: 12px; margin: 22px 0; }
        .chemistry-fact { background: #ffffff; border: 1px solid #e5e7eb; border-radius: 8px; padding: 14px; }
        .chemistry-fact span { display: block; color: #64748b; font-size: 0.82rem; font-weight: 800; }
        .chemistry-fact strong { display: block; color: #111827; line-height: 1.35; margin-top: 6px; }

        .chemistry-toc { display: flex; flex-wrap: wrap; gap: 10px; margin: 18px 0 30px; }
        .chemistry-toc a { background: var(--chem-soft); border: 1px solid var(--chem-line); border-radius: 999px; color: var(--chem-primary); font-size: 0.9rem; font-weight: 800; padding: 8px 12px; text-decoration: none; }

        .chemistry-question { border: 1px solid #e5e7eb; border-left: 4px solid var(--chem-primary); border-radius: 8px; background: #ffffff; padding: 16px; margin: 18px 0; }
        .chemistry-answer { background: #f8fafc; border-radius: 8px; color: #334155; line-height: 1.75; margin-top: 12px; padding: 14px; }
        
        .chemistry-download-panel { align-items: center; background: #ffffff; border: 1px solid var(--chem-line); border-radius: 10px; display: flex; flex-wrap: wrap; gap: 14px; justify-content: space-between; margin: 18px 0 24px; padding: 16px; }
        .chemistry-coin-btn { background: var(--chem-primary); border: 0; border-radius: 8px; color: #ffffff; cursor: pointer; font-weight: 800; padding: 11px 16px; }
        .chemistry-coin-btn:hover { background: #357abd; }
        
        .chemistry-chapter-nav { display: grid; grid-template-columns: repeat(auto-fit, minmax(180px, 1fr)); gap: 10px; margin-top: 18px; }
        .chemistry-chapter-nav a { background: #ffffff; border: 1px solid #e5e7eb; border-radius: 8px; color: #1f2937; font-weight: 800; padding: 12px; text-decoration: none; }
        .chemistry-chapter-nav a.active, .chemistry-chapter-nav a:hover { background: var(--chem-soft); border-color: var(--chem-primary); color: var(--chem-primary); }

        .concept-list { padding-left: 20px; }
        .concept-list li { margin-bottom: 8px; }
        .word-table { width: 100%; border-collapse: collapse; margin-top: 10px; }
        .word-table th, .word-table td { border: 1px solid #e5e7eb; padding: 10px; text-align: left; }
        .word-table th { background-color: var(--chem-soft); color: var(--chem-ink); }

        body.dark-mode .chemistry-hero { background: linear-gradient(135deg, #111827 0%, #0f172a 56%, #1e293b 100%) !important; border-color: #334155 !important; }
        body.dark-mode .chemistry-hero h1, body.dark-mode .chemistry-fact strong { color: #f8fafc !important; }
        body.dark-mode .chemistry-hero p, body.dark-mode .chemistry-answer { color: #cbd5e1 !important; }
        body.dark-mode .chemistry-fact, body.dark-mode .chemistry-question, body.dark-mode .chemistry-answer, body.dark-mode .chemistry-download-panel, body.dark-mode .chemistry-chapter-nav a { background: rgba(17, 24, 39, 0.94) !important; border-color: #334155 !important; }