:root {
            --primary: #0066aa;
            --primary-dark: #004b7a;
            --primary-light: #e6f4ff;
            --accent: #00a3d9;
            --bg: #f5f9fc;
            --text: #1f2933;
            --muted: #6b7280;
            --border: #d1d5db;
            --max-width: 1100px;
            --radius-lg: 10px;
            --radius-md: 6px;
        }

        * {
            box-sizing: border-box;
        }

        html {
            scroll-behavior: smooth;
        }

        body {
            margin: 0;
            font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
            color: var(--text);
            background: radial-gradient(circle at top, #e6f4ff 0, #f9fbff 45%, #f5f9fc 100%);
            line-height: 1.6;
        }

        main {
            max-width: var(--max-width);
            margin: 1.8rem auto 3rem;
            padding: 0 1.5rem 2rem;
        }

        .hero {
            background: #ffffff;
            border-radius: 20px;
            padding: 1.8rem 1.6rem;
            box-shadow: 0 18px 40px rgba(15,23,42,0.15);
            position: relative;
            overflow: hidden;
        }

        .hero::before {
            content: "";
            position: absolute;
            inset: -40%;
            background: radial-gradient(circle at top left, rgba(255,255,255,0.65) 0, transparent 55%),
                        radial-gradient(circle at top right, rgba(59,130,246,0.18) 0, transparent 60%);
            opacity: 0.8;
            pointer-events: none;
        }

        .hero-inner {
            position: relative;
            z-index: 1;
        }

        .hero-title {
            font-size: clamp(1.7rem, 4vw, 2.1rem);
            margin: 0 0 0.5rem;
            color: var(--primary-dark);
        }

        .hero-subtitle {
            margin: 0;
            font-size: 0.98rem;
            color: var(--muted);
            max-width: 600px;
        }

        .meta-grid {
            margin-top: 1.3rem;
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(190px, 1fr));
            gap: 0.9rem;
        }

        .meta-card {
            background: linear-gradient(135deg, #f1f5f9, #e0f2fe);
            border-radius: 14px;
            padding: 0.85rem 0.95rem;
            border: 1px solid rgba(148,163,184,0.4);
            font-size: 0.86rem;
            color: #0f172a;
            display: flex;
            flex-direction: column;
            gap: 0.1rem;
        }

        .meta-label {
            font-weight: 600;
            letter-spacing: 0.04em;
            text-transform: uppercase;
            font-size: 0.7rem;
            color: #64748b;
        }

        .notice {
            margin-top: 1.1rem;
            padding: 0.75rem 0.9rem;
            border-radius: 12px;
            background: rgba(59,130,246,0.05);
            border: 1px dashed rgba(37,99,235,0.4);
            font-size: 0.85rem;
            color: #1e293b;
        }

        .notice strong {
            color: var(--primary-dark);
        }

        .content-grid {
            display: grid;
            grid-template-columns: minmax(0, 280px) minmax(0, 1.6fr);
            gap: 1.6rem;
            margin-top: 1.8rem;
        }

        nav#toc {
            position: sticky;
            top: 95px;
            align-self: flex-start;
        }

        .toc-card {
            background: #ffffff;
            border-radius: 16px;
            padding: 1.1rem 1rem;
            box-shadow: 0 12px 30px rgba(15,23,42,0.12);
            border: 1px solid rgba(148,163,184,0.45);
        }

        .toc-title {
            font-size: 0.95rem;
            font-weight: 600;
            margin-top: 0;
            margin-bottom: 0.4rem;
            color: var(--primary-dark);
        }

        .toc-subtitle {
            font-size: 0.8rem;
            color: var(--muted);
            margin-bottom: 0.7rem;
        }

        .toc-list {
            list-style: none;
            padding-left: 0;
            margin: 0;
        }

        .toc-list > li {
            margin-bottom: 0.35rem;
            font-size: 0.85rem;
        }

        .toc-link {
            text-decoration: none;
            color: var(--primary-dark);
            padding: 0.2rem 0.3rem;
            border-radius: 6px;
            display: block;
            border-left: 3px solid transparent;
            transition: all 0.18s ease;
        }

        .toc-link:hover {
            background: rgba(59,130,246,0.07);
            border-left-color: var(--accent);
            transform: translateX(1px);
        }

        .toc-sublist {
            list-style: none;
            padding-left: 0.8rem;
            margin-top: 0.2rem;
        }

        .toc-sublist li {
            font-size: 0.8rem;
            margin-bottom: 0.22rem;
        }

        .toc-sublist .toc-link {
            color: #4b5563;
            border-left-width: 2px;
        }

        .section {
            background: #ffffff;
            border-radius: 18px;
            padding: 1rem 1.5rem;
            margin-bottom: 1.1rem;
            box-shadow: 0 10px 26px rgba(15,23,42,0.12);
            border: 1px solid rgba(148,163,184,0.45);
            scroll-margin-top: 90px;
        }

        .section-header {
            display: flex;
            align-items: baseline;
            gap: 0.4rem;
            margin-bottom: 0.7rem;
            flex-wrap: wrap;
        }

        .section-number {
            font-weight: 700;
            color: var(--accent);
            font-size: 0.95rem;
            letter-spacing: 0.06em;
            text-transform: uppercase;
        }

        .section-title {
            font-size: 1.1rem;
            margin: 0;
            color: var(--primary-dark);
        }

        .section h3 {
            font-size: 0.98rem;
            margin-top: 1.1rem;
            margin-bottom: 0.25rem;
            color: #111827;
        }

        p {
            margin: 0.25rem 0 0.35rem;
            font-size: 0.92rem;
        }

        ul {
            margin: 0.3rem 0 0.4rem 1.1rem;
            padding-left: 0.2rem;
            font-size: 0.9rem;
        }

        li {
            margin-bottom: 0.15rem;
        }

        code {
            font-family: "SF Mono", ui-monospace, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace;
            font-size: 0.85em;
            background: rgba(15,23,42,0.04);
            padding: 0.08rem 0.25rem;
            border-radius: 4px;
        }

        a {
            color: var(--primary-dark);
        }

        a:hover {
            color: #1d4ed8;
        }

        footer {
            background: #0b1120;
            color: #9ca3af;
            padding: 1.5rem 1.5rem 2rem;
            margin-top: 1rem;
        }

        .footer-inner {
            max-width: var(--max-width);
            margin: 0 auto;
            font-size: 0.8rem;
            display: flex;
            flex-wrap: wrap;
            gap: 0.75rem 2rem;
            align-items: center;
            justify-content: space-between;
        }

        .footer-inner a {
            color: #e5e7eb;
            text-decoration: none;
        }

        .footer-inner a:hover {
            color: #ffffff;
            text-decoration: underline;
        }

        .footer-meta {
            opacity: 0.8;
        }

        @media (max-width: 920px) {
            .content-grid {
                grid-template-columns: minmax(0, 1fr);
            }
            nav#toc {
                position: static;
            }
        }

        @media (max-width: 640px) {
            header {
                padding: 0.85rem 1.1rem;
            }
            .header-inner {
                flex-direction: column;
                align-items: flex-start;
            }
            .back-link {
                align-self: flex-end;
            }
            main {
                padding: 0 1.1rem 1.6rem;
                margin-top: 1.1rem;
            }
            .hero {
                padding: 1.4rem 1.1rem;
            }
            .section {
                padding: 1.1rem 1.1rem 1rem;
            }
        }