:root {
            color-scheme: light;
            font-size: 16px;
        }
        body {
            margin: 0;
            min-height: 100vh;
            font-family: "Segoe UI", "Helvetica Neue", Arial, sans-serif;
            color: #202124;
            background: #f5f7fb;
            line-height: 1.7;
            font-size: clamp(1rem, 0.98rem + 0.3vw, 1.1rem);
            display: flex;
            flex-direction: column;
        }
        body > header,
        body > nav.book-nav,
        body > main,
        body > footer {
            width: min(960px, 92vw);
            margin: 0 auto;
        }
        body > main {
            margin-top: clamp(1.2rem, 3vw, 1.8rem);
        }
        body > header,
        body > footer {
            padding: clamp(1rem, 3vw, 1.75rem) 0;
        }
        header.book-header .page-title {
            margin: 0 0 0.35rem;
            font-size: clamp(2rem, 4vw, 2.5rem);
            font-weight: 700;
        }
header.book-header .page-subtitle {
    margin: 0;
    color: #4b5c6b;
}

.site-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1rem 0;
}
.site-header .brand {
    font-size: clamp(1.4rem, 3vw, 1.8rem);
    font-weight: 700;
    color: #132f52;
    text-decoration: none;
}
.site-links {
    display: flex;
    gap: 1rem;
    align-items: center;
}
.site-links a {
    text-decoration: none;
    font-weight: 600;
    color: #1a4d7a;
}
.nav-toggle {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    background: none;
    border: 0;
    font-size: 1.1rem;
    cursor: pointer;
    color: #1a4d7a;
}
.toc-drawer {
    position: relative;
}
.toc-drawer nav {
    background: #ffffff;
    border: 1px solid #dce5f4;
    border-radius: 12px;
    padding: 1rem;
    box-shadow: 0 18px 48px rgba(15, 23, 42, 0.12);
    position: absolute;
    right: 0;
    top: 100%;
    width: min(360px, 85vw);
    max-height: 75vh;
    overflow-y: auto;
    padding: 1.2rem 1.1rem 2rem;
    display: none;
    z-index: 15;
}
.toc-drawer.open nav {
    display: block;
}
.toc-drawer nav .toc-group {
    margin-bottom: 1.2rem;
}
.toc-drawer nav .toc-group h3 {
    margin: 0 0 0.5rem;
    font-size: 1rem;
    color: #1a4d7a;
    text-transform: uppercase;
    letter-spacing: 0.04em;
}
.toc-drawer nav ul {
    list-style: none;
    padding: 0;
    margin: 0;
    display: grid;
    gap: 0.5rem;
}
.toc-drawer nav a {
    color: #132f52;
    text-decoration: none;
    font-weight: 500;
}
@media (max-width: 860px) {
    .site-links {
        display: none;
    }
    .nav-toggle {
        display: block;
    }
}
nav.book-nav {
    position: sticky;
    top: 0;
    z-index: 40;
    display: flex;
    align-items: center;
    gap: 0.6rem;
    padding: clamp(0.55rem, 2vw, 0.8rem) clamp(1rem, 4vw, 1.5rem);
    margin: 0;
    background: #ffffff;
    border-bottom: 1px solid #dce5f4;
    box-shadow: 0 6px 18px rgba(15, 23, 42, 0.08);
}
nav.book-nav .nav-links {
    display: flex;
    flex: 1;
    justify-content: flex-end;
    padding: 0 0.5rem;
    box-sizing: border-box;
    align-items: center;
    flex-wrap: nowrap;
    gap: 0.6rem;
    overflow-x: auto;
}
nav.book-nav .nav-toggle,
nav.book-nav .nav-link {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 0.45rem;
    padding: 0.45rem 0.75rem;
    min-width: 4.2rem;
    border-radius: 999px;
    border: 1px solid #cbd8ea;
    background: #f5f7fb;
    color: #1f3d63;
    font-weight: 600;
    text-decoration: none;
    transition: background 0.15s ease, box-shadow 0.15s ease;
}
nav.book-nav .nav-toggle {
    cursor: pointer;
    background: #ffffff;
}
nav.book-nav .nav-link.disabled {
    cursor: default;
    pointer-events: none;
    opacity: 0.45;
}
nav.book-nav .nav-toggle:hover,
nav.book-nav .nav-toggle:focus-visible,
nav.book-nav .nav-link:hover,
nav.book-nav .nav-link:focus-visible {
    background: #e4edff;
    box-shadow: 0 3px 12px rgba(31, 61, 99, 0.2);
}
.nav-panel {
    position: fixed;
    top: 0;
    left: 0;
    height: 100vh;
    width: min(22rem, 90vw);
    background: #ffffff;
    border-right: 1px solid #dce5f4;
    box-shadow: 12px 0 40px rgba(15, 23, 42, 0.18);
    padding: 1.2rem 1.1rem 3.5rem;
    display: flex;
    flex-direction: column;
    gap: 1.6rem;
    transform: translateX(-100%);
    transition: transform 0.25s ease;
    z-index: 60;
    overflow-y: auto;
}
.nav-panel.open {
    transform: translateX(0);
}
.nav-panel__group {
    margin: 0;
}
.nav-panel__group:last-child {
    padding-bottom: 1rem;
}
.nav-panel__title {
    margin: 0 0 0.85rem;
    font-size: 0.95rem;
    letter-spacing: 0.05em;
    text-transform: uppercase;
    color: #1f3d63;
}
.nav-panel__list {
    list-style: none;
    margin: 0;
    padding: 0;
    display: grid;
    gap: 0.65rem;
}
.nav-panel__link,
.nav-panel__link.disabled {
    display: inline-flex;
    align-items: center;
    gap: 0.45rem;
    color: #223a5d;
    text-decoration: none;
    font-weight: 600;
    line-height: 1.25;
}
.nav-panel__link.disabled {
    color: #9aa6bf;
    cursor: default;
    pointer-events: none;
}
.nav-panel__link.is-active {
    color: #0f326e;
    font-weight: 700;
}
.nav-panel__link:hover,
.nav-panel__link:focus-visible {
    text-decoration: underline;
}
.page-toc {
    border: 1px solid #dce5f4;
    background: #ffffff;
    border-radius: 12px;
    margin-bottom: clamp(1.5rem, 4vw, 2.4rem);
    box-shadow: 0 12px 28px rgba(15, 23, 42, 0.08);
    overflow: hidden;
}
.page-toc__toggle {
    width: 100%;
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 0.75rem;
    padding: 0.65rem 0.95rem;
    border: none;
    background: transparent;
    font-weight: 600;
    font-size: 0.95rem;
    color: #1f3d63;
    cursor: pointer;
}
.page-toc__toggle .icon {
    transition: transform 0.18s ease;
}
.page-toc.open .page-toc__toggle .icon {
    transform: rotate(90deg);
}
.page-toc__panel {
    display: none;
    padding: 0 1.1rem 1.1rem;
}
.page-toc.open .page-toc__panel {
    display: block;
}
.page-toc__list {
    list-style: none;
    margin: 0;
    padding: 0;
    display: grid;
    gap: 0.55rem;
}
.page-toc__list > li > a,
.page-toc__list > li > span {
    color: #1f3d63;
    text-decoration: none;
    font-weight: 600;
}
.page-toc__list > li > a:hover,
.page-toc__list > li > a:focus-visible {
    text-decoration: underline;
}
.page-toc__sublist {
    list-style: none;
    margin: 0.4rem 0 0 0.8rem;
    padding: 0 0 0 0.9rem;
    border-left: 1px solid #e2e9f6;
    display: grid;
    gap: 0.45rem;
}
.page-toc__sublist a {
    color: #34507a;
    text-decoration: none;
    font-weight: 500;
}
.page-toc__sublist a:hover,
.page-toc__sublist a:focus-visible {
    text-decoration: underline;
}
.page-toc .toc-level-2 > .page-toc__sublist {
    margin-top: 0.35rem;
}
.page-toc .toc-level-5,
.page-toc .toc-level-6 {
    display: none;
}
@media (max-width: 720px) {
    nav.book-nav .nav-toggle,
    nav.book-nav .nav-link {
        min-width: 3rem;
        padding: 0.5rem 0.75rem;
    }
    nav.book-nav .nav-toggle .label,
    nav.book-nav .nav-link .label {
        display: none;
    }
    nav.book-nav .nav-link.contents {
        display: none;
    }
    nav.book-nav .nav-links {
        gap: 0.4rem;
    }
}
        main {
            flex: 1;
            background: #ffffff;
        padding: clamp(1.5rem, 4vw, 2.6rem);
        border-radius: 12px;
        box-shadow: 0 16px 40px rgba(15, 23, 42, 0.08);
        margin-bottom: clamp(1.5rem, 5vw, 2.5rem);
        margin-top: clamp(1.5rem, 4vw, 2.4rem);
    }
        main > :first-child {
            margin-top: 0;
        }
        main > :last-child {
            margin-bottom: 0;
        }
        img,
        video,
        iframe {
            max-width: 100%;
            height: auto;
            border-radius: 6px;
        }
        pre {
            overflow-x: auto;
            background: #0f172a;
            color: #e2e8f0;
            padding: 1rem;
            border-radius: 8px;
            font-size: 0.95rem;
        }
        code {
            font-family: "Fira Code", "SFMono-Regular", Menlo, Consolas, monospace;
        }
        blockquote {
            border-left: 4px solid #c8d9ee;
            padding-left: 1rem;
            margin: 1.5rem 0;
            color: #475569;
            background: #f1f6fd;
        }
        .toc-list {
            list-style: none;
            padding: 0;
            margin: 2rem 0;
            display: grid;
            gap: 0.75rem;
        }
        .toc-list a {
            text-decoration: none;
            color: #194877;
            font-weight: 600;
        }
        footer.book-footer {
            margin-top: auto;
            font-size: 0.9rem;
            color: #5f6368;
            text-align: center;
        }
        table {
            border-collapse: collapse;
            width: 100%;
            margin: 1.5rem 0;
        }
        table,
        th,
        td {
            border: 1px solid #c7d3e3;
        }
        th,
        td {
            padding: 0.65rem;
            text-align: left;
        }
        @media (max-width: 600px) {
            body > header,
            body > nav.book-nav,
            body > main,
            body > footer {
                width: min(640px, 94vw);
            }
            main {
                padding: clamp(1.1rem, 5vw, 1.6rem);
                border-radius: 10px;
            }
        }

.page-toc__text { color: #1f3d63; font-weight: 600; }
.page-toc__toggle .label { order: 0; }
.page-toc__toggle .icon { order: 1; transform: rotate(0deg); transition: transform 0.18s ease; }
.page-toc.open .page-toc__toggle .icon { transform: rotate(90deg); }
.back-to-top {
    position: fixed;
    right: clamp(1rem, 4vw, 1.75rem);
    bottom: clamp(1.2rem, 4vw, 2rem);
    width: 3rem;
    height: 3rem;
    border-radius: 50%;
    border: none;
    background: #1f3d63;
    color: #ffffff;
    font-size: 1.35rem;
    font-weight: 600;
    display: flex;
    align-items: center;
    justify-content: center;
    box-shadow: 0 12px 25px rgba(15, 23, 42, 0.25);
    cursor: pointer;
    opacity: 0;
    visibility: hidden;
    transition: opacity 0.2s ease, visibility 0.2s ease, transform 0.2s ease;
    z-index: 80;
}
.back-to-top.visible {
    opacity: 1;
    visibility: visible;
}
.back-to-top:focus-visible,
.back-to-top:hover {
    background: #0f326e;
    transform: translateY(-2px);
}
.chapter-quiz {
    margin-top: clamp(2.8rem, 6vw, 3.8rem);
    border-top: 1px solid #d9e4f5;
    padding-top: clamp(1.8rem, 5vw, 2.6rem);
}
.chapter-quiz__heading {
    margin: 0;
    font-size: clamp(1.25rem, 3vw, 1.6rem);
    color: #102a4c;
    font-weight: 700;
}
.chapter-quiz__app {
    margin-top: clamp(1.2rem, 4vw, 1.8rem);
}
.chapter-quiz__card {
    background: #ffffff;
    border-radius: 16px;
    border: 1px solid #dce5f4;
    box-shadow: 0 18px 40px rgba(15, 23, 42, 0.08);
    padding: clamp(1.5rem, 4vw, 2.2rem);
    display: grid;
    gap: clamp(1rem, 3vw, 1.4rem);
}
.chapter-quiz__meta {
    font-size: 0.95rem;
    color: #4b5c6b;
    letter-spacing: 0.04em;
    text-transform: uppercase;
    margin: 0;
}
.chapter-quiz__question {
    margin: 0;
    font-size: clamp(1.15rem, 2.6vw, 1.55rem);
    font-weight: 700;
    color: #132f52;
}
.chapter-quiz__options {
    border: none;
    padding: 0;
    margin: 0;
    display: grid;
    gap: 0.9rem;
}
.chapter-quiz__option {
    border: 1px solid #c7d3e3;
    border-radius: 12px;
    padding: 0.85rem 1rem;
    display: flex;
    align-items: flex-start;
    gap: 0.75rem;
    background: #f8fbff;
    transition: border 0.15s ease, background 0.15s ease;
}
.chapter-quiz__option input[type="radio"] {
    margin-top: 0.35rem;
}
.chapter-quiz__option:hover {
    border-color: #2563eb;
    background: #edf3ff;
}
.chapter-quiz__alert {
    background: #fef3c7;
    color: #92400e;
    padding: 0.85rem 1rem;
    border-radius: 12px;
    display: none;
}
.chapter-quiz__actions {
    display: flex;
    flex-wrap: wrap;
    gap: 0.8rem;
    justify-content: flex-end;
}
.chapter-quiz__button {
    font-family: inherit;
    font-weight: 600;
    border: none;
    border-radius: 999px;
    padding: 0.65rem 1.6rem;
    cursor: pointer;
    transition: transform 0.15s ease, box-shadow 0.15s ease, background 0.15s ease;
}
.chapter-quiz__button--primary {
    background: linear-gradient(135deg, #2563eb, #1d4ed8);
    color: #ffffff;
    box-shadow: 0 10px 20px rgba(37, 99, 235, 0.22);
}
.chapter-quiz__button--secondary {
    background: #e6f0fb;
    color: #1a4d7a;
    box-shadow: 0 6px 16px rgba(26, 77, 122, 0.18);
}
.chapter-quiz__button:disabled {
    opacity: 0.6;
    cursor: not-allowed;
    box-shadow: none;
}
.chapter-quiz__button:hover:not(:disabled) {
    transform: translateY(-2px);
    box-shadow: 0 14px 28px rgba(26, 77, 122, 0.28);
}
.chapter-quiz__button:focus-visible {
    outline: 3px solid #2563eb;
    outline-offset: 2px;
}
.chapter-quiz__tip {
    margin: 0;
    color: #4b5c6b;
    font-size: 0.95rem;
}
.chapter-quiz__loading,
.chapter-quiz__error {
    font-size: 1rem;
    color: #4b5c6b;
    background: #f8fbff;
    border: 1px solid #dce5f4;
    border-radius: 12px;
    padding: 1rem 1.2rem;
}
.chapter-quiz__error {
    color: #991b1b;
    background: #fee2e2;
    border-color: #fecaca;
}
.chapter-quiz__score {
    padding: 1rem 1.3rem;
    border-radius: 12px;
    font-weight: 600;
    display: flex;
    flex-direction: column;
    gap: 0.35rem;
}
.chapter-quiz__score--high {
    background: #d1fae5;
    color: #065f46;
}
.chapter-quiz__score--mid {
    background: #fef9c3;
    color: #92400e;
}
.chapter-quiz__score--low {
    background: #fee2e2;
    color: #991b1b;
}
.chapter-quiz__review {
    display: grid;
    gap: 1.1rem;
    margin-top: 1.5rem;
}
.chapter-quiz__review-item {
    border: 1px solid #dce5f4;
    border-radius: 12px;
    background: #ffffff;
    padding: 1rem 1.2rem;
}
.chapter-quiz__review-item.correct {
    border-color: #a7f3d0;
    background: #ecfdf5;
}
.chapter-quiz__review-item.incorrect {
    border-color: #fecaca;
    background: #fef2f2;
}
.chapter-quiz__review-item h4 {
    margin: 0 0 0.35rem;
    font-size: 1.05rem;
    color: #132f52;
}
.chapter-quiz__review-item p {
    margin: 0.35rem 0;
}
.chapter-quiz__noscript {
    display: block;
    margin-top: 1rem;
    color: #991b1b;
    font-weight: 600;
}
.chapter-quiz__actions--center {
    justify-content: center;
}
@media (max-width: 640px) {
    .chapter-quiz__actions {
        justify-content: center;
    }
}