/* Extracted from guides/subtractive-synthesis-guide.html — keep in sync if structure changes. */
        .synth-hero {
            background: linear-gradient(135deg, rgba(0, 212, 255, 0.05), rgba(139, 92, 246, 0.05));
            border-bottom: 1px solid var(--border-color);
            padding: 4rem 0;
            text-align: center;
            position: relative;
            z-index: 2;
        }

        .synth-hero h1 {
            font-size: 2.5rem;
            margin-bottom: 0.5rem;
            background: linear-gradient(135deg, var(--primary-color), var(--accent-purple));
            -webkit-background-clip: text;
            -webkit-text-fill-color: transparent;
            background-clip: text;
        }

        .synth-hero p {
            color: var(--muted-text);
            font-size: 1.1rem;
        }

        .section-card {
            background: linear-gradient(135deg, rgba(0, 212, 255, 0.05), rgba(139, 92, 246, 0.05));
            border: 2px solid var(--border-color);
            padding: 2rem;
            margin-bottom: 2rem;
            border-radius: 12px;
            transition: var(--transition);
            box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
        }

        .section-card:hover {
            border-color: var(--primary-color);
            box-shadow: 0 6px 12px rgba(0, 212, 255, 0.2);
        }

        .section-card h3 {
            color: var(--primary-color);
            margin-bottom: 1.5rem;
            font-size: 1.8rem;
            padding-bottom: 0.75rem;
            border-bottom: 3px solid var(--primary-color);
            display: inline-block;
            width: 100%;
        }

        .section-card h4 {
            color: var(--primary-color);
            margin-top: 2rem;
            margin-bottom: 1rem;
            font-size: 1.3rem;
            padding-left: 0.5rem;
            border-left: 4px solid var(--secondary-color);
        }

        .section-card p {
            color: var(--muted-text);
            line-height: 1.8;
            margin-bottom: 1.2rem;
        }

        .section-card ul {
            color: var(--muted-text);
            line-height: 2;
            margin-left: 1.5rem;
        }

        .section-card li {
            margin-bottom: 1rem;
            padding-left: 0.5rem;
        }

        .section-card li::marker {
            color: var(--primary-color);
            font-weight: bold;
        }

        .parameter-box {
            background: linear-gradient(135deg, rgba(0, 212, 255, 0.1), rgba(139, 92, 246, 0.1));
            border-left: 5px solid var(--primary-color);
            border-radius: 8px;
            padding: 1.5rem;
            margin: 2rem 0;
            box-shadow: inset 0 2px 4px rgba(0, 0, 0, 0.05);
        }

        .parameter-box strong {
            color: var(--primary-color);
            font-size: 1.05rem;
        }

        .tips-box {
            background: linear-gradient(135deg, rgba(139, 92, 246, 0.1), rgba(0, 212, 255, 0.05));
            border-left: 5px solid var(--accent-purple);
            border-radius: 8px;
            padding: 1.5rem;
            margin: 2rem 0;
            box-shadow: inset 0 2px 4px rgba(0, 0, 0, 0.05);
        }

        .tips-box strong {
            color: var(--accent-purple);
        }

        .back-link {
            margin-bottom: 2rem;
        }

        .back-link a {
            color: var(--primary-color);
            text-decoration: none;
            display: inline-flex;
            align-items: center;
            gap: 5px;
            font-weight: 500;
            transition: var(--transition);
        }

        .back-link a:hover {
            color: var(--secondary-color);
        }

        @media (max-width: 768px) {
            .synth-hero h1 { font-size: 1.8rem; }
        }

        .toc-nav {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(140px, 1fr));
            gap: 1rem;
            margin: 2rem 0 3rem;
            padding: 0;
        }

        .toc-item {
            display: flex;
            flex-direction: column;
            align-items: center;
            text-align: center;
            padding: 1.2rem 0.8rem;
            background: linear-gradient(135deg, rgba(0, 212, 255, 0.06), rgba(139, 92, 246, 0.06));
            border: 1px solid var(--border-color);
            border-radius: 10px;
            text-decoration: none;
            color: var(--muted-text);
            transition: var(--transition);
            font-size: 0.85rem;
            line-height: 1.3;
        }

        .toc-item:hover {
            border-color: var(--primary-color);
            transform: translateY(-4px);
            box-shadow: 0 8px 20px rgba(0, 212, 255, 0.15);
            color: var(--primary-color);
        }

        .toc-icon {
            font-size: 2rem;
            margin-bottom: 0.5rem;
            display: block;
        }

        @media (max-width: 480px) {
            .toc-nav { grid-template-columns: repeat(2, 1fr); }
        }

        /* ─── CSS Waveform Illustrations ─── */
        .waveform-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
            gap: 1.5rem;
            margin: 2rem 0;
        }

        .waveform-card {
            background: rgba(0, 0, 0, 0.2);
            border: 1px solid var(--border-color);
            border-radius: 10px;
            padding: 1.2rem;
            text-align: center;
        }

        .waveform-card h5 {
            color: var(--primary-color);
            margin-bottom: 0.5rem;
            font-size: 1rem;
        }

        .waveform-card p {
            font-size: 0.85rem;
            margin-bottom: 0.5rem;
        }

        .waveform-card svg {
            width: 100%;
            height: 60px;
            display: block;
            margin: 0.5rem auto;
        }

        /* ─── Signal Flow Diagram ─── */
        .signal-flow-diagram {
            display: flex;
            flex-wrap: wrap;
            align-items: center;
            justify-content: center;
            gap: 0.5rem;
            margin: 2rem 0;
            padding: 1.5rem;
            background: rgba(0, 0, 0, 0.15);
            border-radius: 12px;
            border: 1px solid var(--border-color);
        }

        .flow-block {
            background: linear-gradient(135deg, rgba(0, 212, 255, 0.15), rgba(139, 92, 246, 0.15));
            border: 2px solid var(--primary-color);
            border-radius: 10px;
            padding: 0.8rem 1.2rem;
            text-align: center;
            min-width: 100px;
            color: var(--primary-color);
            font-weight: 600;
            font-size: 0.9rem;
        }

        .flow-block .flow-icon {
            font-size: 1.5rem;
            display: block;
            margin-bottom: 0.3rem;
        }

        .flow-arrow {
            color: var(--accent-purple);
            font-size: 1.5rem;
            font-weight: bold;
        }

        .flow-mod {
            background: rgba(139, 92, 246, 0.1);
            border: 2px dashed var(--accent-purple);
            border-radius: 10px;
            padding: 0.6rem 1rem;
            text-align: center;
            color: var(--accent-purple);
            font-size: 0.8rem;
            font-weight: 500;
        }

        .flow-mod-row {
            display: flex;
            flex-wrap: wrap;
            align-items: center;
            justify-content: center;
            gap: 0.8rem;
            margin-top: 1rem;
            width: 100%;
        }

        @media (max-width: 600px) {
            .signal-flow-diagram { flex-direction: column; }
            .flow-arrow { transform: rotate(90deg); }
        }

        /* ─── ADSR Diagram ─── */
        .adsr-diagram svg {
            width: 100%;
            max-width: 500px;
            height: 180px;
            display: block;
            margin: 1.5rem auto;
        }

        /* ─── Synth Types Comparison Table ─── */
        .synth-table {
            width: 100%;
            border-collapse: collapse;
            margin: 1.5rem 0;
            font-size: 0.9rem;
        }

        .synth-table th,
        .synth-table td {
            padding: 0.8rem 1rem;
            border: 1px solid var(--border-color);
            text-align: left;
        }

        .synth-table th {
            background: linear-gradient(135deg, rgba(0, 212, 255, 0.15), rgba(139, 92, 246, 0.15));
            color: var(--primary-color);
            font-weight: 600;
        }

        .synth-table tr:nth-child(even) {
            background: rgba(0, 0, 0, 0.1);
        }

        .synth-table td:first-child {
            font-weight: 600;
            color: var(--primary-color);
        }

        @media (max-width: 600px) {
            .synth-table { font-size: 0.78rem; }
            .synth-table th, .synth-table td { padding: 0.5rem; }
        }

        /* ─── Exercise Cards ─── */
        .exercise-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
            gap: 1.5rem;
            margin: 2rem 0;
        }

        .exercise-card {
            background: rgba(0, 0, 0, 0.15);
            border: 1px solid var(--border-color);
            border-radius: 10px;
            padding: 1.5rem;
            transition: var(--transition);
        }

        .exercise-card:hover {
            border-color: var(--accent-purple);
            box-shadow: 0 4px 12px rgba(139, 92, 246, 0.15);
        }

        .exercise-card h5 {
            color: var(--accent-purple);
            margin-bottom: 0.5rem;
            font-size: 1rem;
        }

        .exercise-card p {
            font-size: 0.9rem;
            line-height: 1.6;
        }

        .exercise-card ol {
            color: var(--muted-text);
            margin-left: 1.2rem;
            line-height: 1.8;
        }

        /* ─── Patch Building Visual Timeline ─── */
        .patch-timeline {
            display: flex;
            flex-wrap: wrap;
            align-items: center;
            justify-content: center;
            gap: 0.3rem;
            margin: 2rem 0;
            padding: 1.5rem;
            background: rgba(0, 0, 0, 0.15);
            border-radius: 12px;
            border: 1px solid var(--border-color);
        }

        .patch-step-node {
            display: flex;
            flex-direction: column;
            align-items: center;
            text-align: center;
            min-width: 70px;
            gap: 0.3rem;
        }

        .patch-step-num {
            width: 36px;
            height: 36px;
            border-radius: 50%;
            background: linear-gradient(135deg, var(--primary-color), var(--accent-purple));
            display: flex;
            align-items: center;
            justify-content: center;
            color: #fff;
            font-weight: bold;
            font-size: 0.85rem;
        }

        .patch-step-label {
            font-size: 0.72rem;
            color: var(--muted-text);
            max-width: 80px;
        }

        .patch-step-arrow {
            color: var(--primary-color);
            font-size: 1.3rem;
            font-weight: bold;
        }

        html[dir="rtl"] .flow-arrow,
        html[dir="rtl"] .patch-step-arrow {
            display: inline-block;
            transform: scaleX(-1);
        }

        @media (max-width: 600px) {
            html[dir="rtl"] .flow-arrow { transform: rotate(90deg); }
        }

        @media (max-width: 480px) {
            .patch-timeline { gap: 0.2rem; }
            .patch-step-node { min-width: 55px; }
            .patch-step-num { width: 28px; height: 28px; font-size: 0.75rem; }
        }

        /* ─── Synth Panel Quick Reference ─── */
        .synth-panel {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
            gap: 1rem;
            margin: 2rem 0;
            padding: 1.5rem;
            background: linear-gradient(180deg, rgba(0, 0, 0, 0.25), rgba(0, 0, 0, 0.12));
            border-radius: 12px;
            border: 2px solid var(--border-color);
        }

        .panel-module {
            text-align: center;
            padding: 1rem 0.8rem;
            background: rgba(0, 0, 0, 0.2);
            border-radius: 8px;
            border: 1px solid var(--border-color);
        }

        .panel-module h6 {
            color: var(--primary-color);
            font-size: 0.8rem;
            margin-bottom: 0.6rem;
            text-transform: uppercase;
            letter-spacing: 0.5px;
        }

        .panel-setting {
            color: var(--accent-purple);
            font-weight: 600;
            font-size: 0.9rem;
            margin: 0.3rem 0;
        }

        .panel-detail {
            color: var(--muted-text);
            font-size: 0.8rem;
            margin: 0.2rem 0;
        }

        .panel-module svg {
            width: 100%;
            max-width: 120px;
            height: 30px;
            display: block;
            margin: 0.5rem auto;
        }

        /* ─── Enhanced Exercise Cards ─── */
        .exercise-card .exercise-goal {
            font-style: italic;
            color: var(--primary-color);
            margin-bottom: 0.8rem;
            font-size: 0.9rem;
        }

        .exercise-card .exercise-learn {
            background: rgba(139, 92, 246, 0.08);
            border-radius: 6px;
            padding: 0.8rem;
            margin-top: 0.8rem;
        }

        .exercise-card .exercise-learn strong {
            color: var(--accent-purple);
            font-size: 0.85rem;
        }

        .exercise-card .exercise-learn p {
            font-size: 0.85rem;
            margin: 0.3rem 0 0;
        }

        .congrats-section {
            text-align: center;
            padding: 2rem;
            margin-top: 2rem;
            background: linear-gradient(135deg, rgba(0, 212, 255, 0.1), rgba(139, 92, 246, 0.1));
            border-radius: 12px;
            border: 2px solid var(--primary-color);
        }

        .congrats-section h4 {
            color: var(--primary-color);
            font-size: 1.5rem;
            margin-bottom: 0.5rem;
        }

        .congrats-section p {
            color: var(--muted-text);
            line-height: 1.8;
        }

        /* ─── LFO Waveform Cards ─── */
        .lfo-wave-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
            gap: 1rem;
            margin: 1.5rem 0;
        }

        .lfo-wave-card {
            background: rgba(0, 0, 0, 0.2);
            border: 1px solid var(--border-color);
            border-radius: 8px;
            padding: 1rem;
            text-align: center;
        }

        .lfo-wave-card h6 {
            color: var(--accent-purple);
            margin-bottom: 0.3rem;
            font-size: 0.9rem;
        }

        .lfo-wave-card p {
            font-size: 0.8rem;
            margin: 0;
        }

        .lfo-wave-card svg {
            width: 100%;
            height: 40px;
            display: block;
            margin: 0.4rem auto;
        }