/* ============================================================
 * CyberSecCloud /book — Trust Acceleration Knowledge Library
 * Shell stylesheet (DESIGN-A v1.1, 9.78/10)
 *
 * Rules (PLAN §9, DESIGN-A §2b/5.2):
 *   - Zero px values anywhere (0.0625rem substitutes for 1px).
 *   - All tokens bind to /css/base.css; dark/light via [data-theme].
 *   - WCAG AA contrast: body text >= 4.5:1, UI >= 3:1.
 *   - Touch targets >= 2.75rem.
 *   - Reduced motion disables transitions globally.
 * ============================================================ */

/* -----------------------------------------------------------
 * 1) Custom properties — the 20 FROZEN book-shell tokens
 * --------------------------------------------------------- */
:root {
    /* Layout (grid column widths, gutters, sticky header height) */
    --book-col-max: 70ch;
    --book-sidebar-w: 18rem;
    --book-outline-w: 14rem;
    --book-gap: 1.5rem;
    --book-header-h: 3.75rem;

    /* Accent (binds to base.css --color-secondary) */
    --book-accent: var(--color-secondary, #06B6D4);
    --book-accent-soft: color-mix(in oklab, var(--book-accent) 12%, transparent);
    --book-accent-strong: color-mix(in oklab, var(--book-accent) 85%, #000);

    /* Surfaces + text (light defaults; dark overrides below) */
    --book-bg: #ffffff;
    --book-surface: #f9fafb;
    --book-surface-elev: #ffffff;
    --book-fg: #0f172a;
    --book-fg-muted: #475569;
    --book-border: #e2e8f0;

    /* Typography */
    --book-serif: "Source Serif 4", Georgia, "Times New Roman", serif;
    --book-sans: Inter, -apple-system, "Segoe UI", Roboto, sans-serif;
    --book-mono: "JetBrains Mono", ui-monospace, Menlo, Consolas, monospace;
    --book-font-body: 1.0625rem;
    --book-line-height: 1.7;

    /* Radii + transitions */
    --book-radius: var(--radius, 0.5rem);
    --book-radius-lg: 0.875rem;
    --book-transition: 150ms ease;
    --book-transition-long: 250ms cubic-bezier(0.2, 0.8, 0.2, 1);

    /* Shadow + focus */
    --book-shadow: 0 0.25rem 1rem rgba(15, 23, 42, 0.08);
    --book-focus-ring: 0 0 0 0.1875rem color-mix(in oklab, var(--book-accent) 55%, transparent);

    /* Tier colors (bind to SC-1 enum) */
    --book-tier-free: #10b981;
    --book-tier-login: var(--color-primary, #3B82F6);
    --book-tier-paid: #f59e0b;

    /* Spacing scale */
    --book-space-1: 0.25rem;
    --book-space-2: 0.5rem;
    --book-space-3: 0.75rem;
    --book-space-4: 1rem;
    --book-space-5: 1.5rem;
    --book-space-6: 2rem;

    /* Hairline border (substitutes for 1px) */
    --book-border-w: 0.0625rem;
}

[data-theme="dark"] {
    --book-bg: var(--color-bg-dark, #0a0a0a);
    --book-surface: var(--color-bg-card, #111111);
    --book-surface-elev: #161824;
    --book-fg: var(--color-text, #e5e5e5);
    --book-fg-muted: var(--color-text-muted, #a3a3a3);
    --book-border: var(--color-border, #1f1f1f);
    --book-shadow: 0 0.25rem 1rem rgba(0, 0, 0, 0.35);
}

/* -----------------------------------------------------------
 * 2) Reset + base
 * --------------------------------------------------------- */
*,
*::before,
*::after {
    box-sizing: border-box;
}

html {
    min-width: 22.5rem;
}

body {
    margin: 0;
    background: var(--book-bg);
    color: var(--book-fg);
    font-family: var(--book-sans);
    font-size: var(--book-font-body);
    line-height: var(--book-line-height);
    transition: background-color var(--book-transition), color var(--book-transition);
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

img,
svg {
    max-width: 100%;
    height: auto;
}

/* Visually-hidden helper */
.sr-only {
    position: absolute;
    width: 0.0625rem;
    height: 0.0625rem;
    padding: 0;
    margin: -0.0625rem;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border: 0;
}

/* Skip link */
.book-skiplink {
    position: absolute;
    top: 0.5rem;
    left: 0.5rem;
    padding: 0.625rem 1rem;
    background: var(--book-accent);
    color: #ffffff;
    border-radius: var(--book-radius);
    font-weight: 600;
    text-decoration: none;
    z-index: 100;
    transform: translateY(-200%);
    transition: transform var(--book-transition);
}
.book-skiplink:focus,
.book-skiplink:focus-visible {
    transform: translateY(0);
    outline: none;
    box-shadow: var(--book-focus-ring);
}

/* Universal focus ring via :focus-visible */
:focus {
    outline: none;
}
:focus-visible {
    outline: none;
    box-shadow: var(--book-focus-ring);
    border-radius: var(--book-radius);
}

/* -----------------------------------------------------------
 * 3) Shared header mount
 * --------------------------------------------------------- */
.book-shared-header {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: 60;
    height: var(--book-header-h);
    background: var(--book-bg);
    border-bottom: var(--book-border-w) solid var(--book-border);
}

/* -----------------------------------------------------------
 * 4) Toolbar
 * --------------------------------------------------------- */
.book-toolbar {
    display: grid;
    /* book-v1.0.2: breadcrumb moved to center column; toolbar now hosts
       just search + actions. Two-cell grid (was auto 1fr auto). */
    grid-template-columns: 1fr auto;
    align-items: center;
    gap: var(--book-space-3);
    padding: 0.75rem 1rem;
    background: var(--book-surface);
    border-bottom: var(--book-border-w) solid var(--book-border);
    position: sticky;
    top: var(--book-header-h);
    z-index: 40;
}

.book-breadcrumb-wrap {
    min-width: 0;
}
.book-breadcrumb {
    list-style: none;
    padding: 0;
    margin: 0;
    display: flex;
    flex-wrap: wrap;
    gap: 0.375rem;
    align-items: center;
    font-family: var(--book-sans);
    font-size: 0.8125rem;
    letter-spacing: 0.005em;
}
.book-breadcrumb li {
    display: inline-flex;
    align-items: center;
    gap: 0.375rem;
    color: var(--book-fg-muted);
}
.book-breadcrumb li + li::before {
    content: "/";
    color: var(--book-fg-muted);
    margin-inline-end: 0.25rem;
    opacity: 0.6;
}
.book-breadcrumb a {
    color: var(--book-fg);
    text-decoration: none;
    padding: 0.25rem 0.375rem;
    border-radius: 0.25rem;
}
.book-breadcrumb a:hover {
    color: var(--book-accent);
}

.book-toolbar-search {
    position: relative;
    display: flex;
    align-items: center;
    max-width: 28rem;
    width: 100%;
    justify-self: center;
}
.book-toolbar-search input {
    width: 100%;
    min-height: 2.75rem;
    padding: 0.5rem 2.75rem 0.5rem 2.25rem;
    background: var(--book-bg);
    color: var(--book-fg);
    border: var(--book-border-w) solid var(--book-border);
    border-radius: var(--book-radius);
    font: inherit;
    font-size: 0.9375rem;
    transition: border-color var(--book-transition), box-shadow var(--book-transition);
}
.book-toolbar-search input::placeholder {
    color: var(--book-fg-muted);
}
.book-toolbar-search input:focus-visible {
    border-color: var(--book-accent);
    box-shadow: var(--book-focus-ring);
}
.book-search-icon {
    position: absolute;
    left: 0.75rem;
    color: var(--book-fg-muted);
    pointer-events: none;
    font-size: 0.875rem;
}
.book-search-kbd {
    position: absolute;
    right: 0.5rem;
    font-family: var(--book-mono);
    font-size: 0.75rem;
    padding: 0.125rem 0.4375rem;
    background: var(--book-surface-elev);
    color: var(--book-fg-muted);
    border: var(--book-border-w) solid var(--book-border);
    border-radius: 0.25rem;
    pointer-events: none;
}

.book-toolbar-actions {
    display: flex;
    align-items: center;
    gap: 0.375rem;
    justify-self: end;
}

/* Icon-only buttons (touch target >= 2.75rem) */
.book-icon-btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    min-width: 2.75rem;
    min-height: 2.75rem;
    padding: 0.5rem;
    background: transparent;
    border: var(--book-border-w) solid transparent;
    border-radius: var(--book-radius);
    color: var(--book-fg-muted);
    cursor: pointer;
    transition: color var(--book-transition), background-color var(--book-transition), border-color var(--book-transition);
    font-size: 0.9375rem;
}
.book-icon-btn:hover {
    color: var(--book-fg);
    background: var(--book-accent-soft);
    border-color: var(--book-border);
}
.book-icon-btn:focus-visible {
    outline: none;
    box-shadow: var(--book-focus-ring);
}

.book-tree-toggle {
    display: none;
}

.book-tier-badge {
    display: inline-flex;
    align-items: center;
    gap: 0.375rem;
    padding: 0.375rem 0.75rem;
    min-height: 2.25rem;
    border: var(--book-border-w) solid var(--book-border);
    border-radius: 624.9375rem;
    background: var(--book-surface-elev);
    font-size: 0.8125rem;
    font-weight: 500;
    color: var(--book-fg);
    white-space: nowrap;
}
.book-tier-badge-dot {
    width: 0.5rem;
    height: 0.5rem;
    border-radius: 50%;
    background: var(--book-tier-free);
}
.book-tier-badge[data-tier="login"] .book-tier-badge-dot { background: var(--book-tier-login); }
.book-tier-badge[data-tier="paid"] .book-tier-badge-dot { background: var(--book-tier-paid); }
.book-tier-badge[data-tier="anon"] .book-tier-badge-dot { background: var(--book-fg-muted); }

/* -----------------------------------------------------------
 * 5) 3-column grid (>= 56.25rem breakpoint)
 * --------------------------------------------------------- */
.book-grid {
    display: grid;
    grid-template-columns: 1fr;
    grid-template-areas: "reader";
    gap: var(--book-gap);
    max-width: 90rem;
    margin: 0 auto;
    padding: var(--book-space-5) 1rem;
    min-height: calc(100vh - var(--book-header-h) - 7rem);
}

.book-tree {
    grid-area: tree;
    position: fixed;
    top: 0;
    left: 0;
    bottom: 0;
    width: 20rem;
    max-width: 90vw;
    background: var(--book-surface);
    border-right: var(--book-border-w) solid var(--book-border);
    transform: translateX(-100%);
    transition: transform var(--book-transition-long);
    z-index: 70;
    display: flex;
    flex-direction: column;
    padding: 1rem;
    box-shadow: var(--book-shadow);
    overflow-y: auto;
}
.book-tree[data-open="true"] {
    transform: translateX(0);
}

.book-tree-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 0.5rem;
    margin-bottom: 1rem;
    padding-bottom: 0.75rem;
    border-bottom: var(--book-border-w) solid var(--book-border);
}
.book-tree-title {
    font-family: var(--book-sans);
    font-size: 0.8125rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--book-fg-muted);
    margin: 0;
}
.book-tree-close {
    display: inline-flex;
}

.book-tree-list {
    list-style: none;
    padding: 0;
    margin: 0;
    font-family: var(--book-sans);
    font-size: 0.875rem;
    line-height: 1.4;
}
.book-tree-list ul {
    list-style: none;
    padding: 0;
    margin: 0;
}
.book-tree-chapter {
    margin-bottom: 0.5rem;
}
.book-tree-chapter > button {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    width: 100%;
    padding: 0.5rem 0.625rem;
    min-height: 2.75rem;
    background: transparent;
    border: 0;
    border-radius: var(--book-radius);
    color: var(--book-fg);
    text-align: left;
    font: inherit;
    font-weight: 600;
    cursor: pointer;
    transition: background-color var(--book-transition);
}
.book-tree-chapter > button:hover {
    background: var(--book-accent-soft);
}
.book-tree-chapter > button:focus-visible {
    outline: none;
    box-shadow: var(--book-focus-ring);
}
.book-tree-chapter-caret {
    display: inline-flex;
    width: 1rem;
    justify-content: center;
    transition: transform var(--book-transition);
    color: var(--book-fg-muted);
    font-size: 0.75rem;
}
.book-tree-chapter[aria-expanded="true"] .book-tree-chapter-caret {
    transform: rotate(90deg);
}
.book-tree-chapter[aria-expanded="false"] > ul {
    display: none;
}
.book-tree-article {
    margin: 0;
}
.book-tree-article > a {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    padding: 0.4375rem 0.625rem 0.4375rem 2.125rem;
    min-height: 2.25rem;
    color: var(--book-fg-muted);
    text-decoration: none;
    border-radius: var(--book-radius);
    font-size: 0.875rem;
    transition: color var(--book-transition), background-color var(--book-transition);
}
.book-tree-article > a:hover {
    color: var(--book-fg);
    background: var(--book-accent-soft);
}
.book-tree-article[aria-selected="true"] > a {
    color: var(--book-accent);
    background: var(--book-accent-soft);
    font-weight: 600;
}
.book-tree-tier-icon {
    font-size: 0.6875rem;
    opacity: 0.7;
}
.book-tree-tier-icon[data-tier="login"] { color: var(--book-tier-login); }
.book-tree-tier-icon[data-tier="paid"] { color: var(--book-tier-paid); }

.book-tree-skel {
    height: 2rem;
    margin-bottom: 0.5rem;
    border-radius: var(--book-radius);
    background: linear-gradient(
        90deg,
        var(--book-surface-elev) 0%,
        var(--book-border) 50%,
        var(--book-surface-elev) 100%
    );
    background-size: 200% 100%;
    animation: book-skel-shimmer 1.5s ease-in-out infinite;
    list-style: none;
}
@keyframes book-skel-shimmer {
    0% { background-position: 200% 0; }
    100% { background-position: -200% 0; }
}

/* Tree error / empty states */
.book-tree-msg {
    padding: 1rem 0.625rem;
    color: var(--book-fg-muted);
    font-size: 0.875rem;
    text-align: center;
}
.book-tree-msg button {
    margin-top: 0.75rem;
    min-height: 2.75rem;
    padding: 0.5rem 1rem;
    background: var(--book-accent);
    color: #ffffff;
    border: 0;
    border-radius: var(--book-radius);
    font: inherit;
    font-weight: 600;
    cursor: pointer;
}

/* Reader */
.book-reader {
    grid-area: reader;
    min-width: 0;
    outline: none;
}

/* Center-column header (book-v1.0.2): breadcrumb + outline toggle on
   one row above the article. Renders on all viewports; the toggle
   button is desktop-only (hidden under .book-outline-toggle media
   rules below) so the row collapses to just the breadcrumb on mobile. */
.book-reader-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 0.75rem;
    margin-bottom: 0.75rem;
    min-height: 2.75rem;
}
.book-reader-header .book-breadcrumb-wrap {
    flex: 1 1 auto;
    min-width: 0;
}
.book-outline-toggle {
    flex: 0 0 auto;
}
.book-outline-toggle[aria-expanded="false"] {
    color: var(--book-fg);
    background: var(--book-accent-soft);
    border-color: var(--book-border);
}
.book-article {
    background: var(--book-surface-elev);
    border: var(--book-border-w) solid var(--book-border);
    border-radius: var(--book-radius-lg);
    padding: 1.75rem 1.5rem;
    max-width: var(--book-col-max);
    margin: 0 auto;
    font-family: var(--book-serif);
}

.book-eyebrow {
    font-family: var(--book-sans);
    font-size: 0.75rem;
    font-weight: 700;
    letter-spacing: 0.08em;
    text-transform: uppercase;
    color: var(--book-accent);
    margin: 0 0 0.625rem;
}
.book-landing-h1 {
    font-family: var(--book-serif);
    font-weight: 700;
    font-size: 2.25rem;
    line-height: 1.2;
    letter-spacing: -0.01em;
    margin: 0 0 0.75rem;
    color: var(--book-fg);
}
.book-landing-lede {
    font-family: var(--book-serif);
    font-size: 1.0625rem;
    line-height: 1.7;
    color: var(--book-fg-muted);
    margin: 0 0 1.5rem;
    hyphens: auto;
}
.book-landing-chips {
    display: flex;
    flex-wrap: wrap;
    gap: 0.5rem;
    margin-bottom: 1.5rem;
}
.book-chip {
    display: inline-flex;
    align-items: center;
    gap: 0.375rem;
    padding: 0.375rem 0.75rem;
    background: var(--book-accent-soft);
    color: var(--book-fg);
    border: var(--book-border-w) solid var(--book-border);
    border-radius: 624.9375rem;
    font-family: var(--book-sans);
    font-size: 0.8125rem;
    font-weight: 500;
}
.book-landing-hint {
    font-family: var(--book-sans);
    font-size: 0.875rem;
    color: var(--book-fg-muted);
    margin: 0;
}

/* Article body typography */
.book-article h1 {
    font-family: var(--book-serif);
    font-size: 2.25rem;
    line-height: 1.2;
    letter-spacing: -0.01em;
    margin: 0 0 1rem;
    color: var(--book-fg);
    hyphens: none;
}
.book-article h2 {
    font-family: var(--book-serif);
    font-size: 1.625rem;
    line-height: 1.25;
    letter-spacing: -0.005em;
    margin: 2rem 0 0.75rem;
    color: var(--book-fg);
    hyphens: none;
    scroll-margin-top: calc(var(--book-header-h) + 4rem);
}
.book-article h3 {
    font-family: var(--book-serif);
    font-size: 1.25rem;
    line-height: 1.3;
    margin: 1.5rem 0 0.5rem;
    color: var(--book-fg);
    hyphens: none;
    scroll-margin-top: calc(var(--book-header-h) + 4rem);
}
.book-article h4 {
    font-family: var(--book-serif);
    font-size: 1.0625rem;
    line-height: 1.35;
    margin: 1.25rem 0 0.5rem;
    color: var(--book-fg);
}
.book-article p,
.book-article li {
    font-family: var(--book-serif);
    font-size: var(--book-font-body);
    line-height: var(--book-line-height);
    color: var(--book-fg);
    hyphens: auto;
}
.book-article p {
    margin: 0 0 1rem;
}
.book-article ul,
.book-article ol {
    margin: 0 0 1rem;
    padding-left: 1.5rem;
}
.book-article a {
    color: var(--book-accent);
    text-decoration: underline;
    text-decoration-color: color-mix(in oklab, var(--book-accent) 55%, transparent);
    text-underline-offset: 0.1875rem;
    transition: color var(--book-transition);
}
.book-article a:hover {
    color: var(--book-accent-strong);
}
.book-article code {
    font-family: var(--book-mono);
    font-size: 0.9375rem;
    background: var(--book-accent-soft);
    color: var(--book-fg);
    padding: 0.125rem 0.3125rem;
    border-radius: 0.25rem;
}
.book-article pre {
    font-family: var(--book-mono);
    font-size: 0.9375rem;
    line-height: 1.55;
    background: var(--book-surface);
    color: var(--book-fg);
    padding: 1rem;
    border: var(--book-border-w) solid var(--book-border);
    border-radius: var(--book-radius);
    overflow-x: auto;
    margin: 0 0 1rem;
}
.book-article pre code {
    background: transparent;
    padding: 0;
}
.book-article blockquote {
    border-left: 0.1875rem solid var(--book-accent);
    padding: 0.25rem 0 0.25rem 1rem;
    margin: 0 0 1rem;
    color: var(--book-fg-muted);
    font-style: italic;
}
.book-article img,
.book-article svg {
    display: block;
    margin: 0 auto 1rem;
    max-width: 100%;
    height: auto;
    border-radius: var(--book-radius);
}
.book-article figure {
    margin: 0 0 1.5rem;
}
.book-article figcaption {
    font-family: var(--book-sans);
    font-size: 0.875rem;
    color: var(--book-fg-muted);
    text-align: center;
    margin-top: 0.5rem;
}
.book-article table {
    width: 100%;
    border-collapse: collapse;
    margin: 0 0 1rem;
    font-family: var(--book-sans);
    font-size: 0.9375rem;
}
.book-article th,
.book-article td {
    padding: 0.625rem 0.75rem;
    border: var(--book-border-w) solid var(--book-border);
    text-align: left;
}
.book-article th {
    background: var(--book-surface);
    font-weight: 600;
}
.book-article kbd {
    font-family: var(--book-mono);
    font-size: 0.8125rem;
    padding: 0.125rem 0.4375rem;
    background: var(--book-surface);
    color: var(--book-fg);
    border: var(--book-border-w) solid var(--book-border);
    border-radius: 0.25rem;
    box-shadow: 0 0.0625rem 0 var(--book-border);
}

/* Prev / next */
.book-prevnext {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 1rem;
    max-width: var(--book-col-max);
    margin: 2rem auto 0;
}
.book-prevnext[hidden] {
    display: none;
}
.book-prevnext-btn {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    padding: 0.875rem 1rem;
    min-height: 3.25rem;
    background: var(--book-surface-elev);
    border: var(--book-border-w) solid var(--book-border);
    border-radius: var(--book-radius);
    color: var(--book-fg);
    cursor: pointer;
    text-align: left;
    font: inherit;
    font-family: var(--book-sans);
    transition: border-color var(--book-transition), background-color var(--book-transition);
}
.book-prevnext-btn:hover {
    border-color: var(--book-accent);
    background: var(--book-accent-soft);
}
.book-prevnext-btn[disabled] {
    opacity: 0.45;
    cursor: not-allowed;
}
#book-next {
    text-align: right;
    justify-content: flex-end;
}
.book-prevnext-label {
    display: flex;
    flex-direction: column;
    min-width: 0;
}
.book-prevnext-hint {
    font-size: 0.75rem;
    color: var(--book-fg-muted);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}
.book-prevnext-title {
    font-weight: 600;
    font-size: 0.9375rem;
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
}

/* Outline */
.book-outline {
    grid-area: outline;
    min-width: 0;
}
.book-outline-details {
    background: var(--book-surface);
    border: var(--book-border-w) solid var(--book-border);
    border-radius: var(--book-radius);
    padding: 0.75rem 1rem;
}
.book-outline-summary {
    font-family: var(--book-sans);
    font-size: 0.8125rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--book-fg-muted);
    cursor: pointer;
    list-style: none;
    min-height: 2.25rem;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}
.book-outline-summary::-webkit-details-marker { display: none; }
.book-outline-summary::before {
    content: "\203A";
    transition: transform var(--book-transition);
    color: var(--book-fg-muted);
    font-size: 1rem;
    line-height: 1;
}
.book-outline-details[open] .book-outline-summary::before {
    transform: rotate(90deg);
}
.book-outline-list {
    list-style: none;
    padding: 0.75rem 0 0;
    margin: 0;
    font-family: var(--book-sans);
    font-size: 0.8125rem;
    line-height: 1.5;
}
.book-outline-list li {
    margin: 0.25rem 0;
}
.book-outline-list li[data-level="3"] {
    padding-left: 1rem;
}
.book-outline-list a {
    display: block;
    padding: 0.3125rem 0.5rem;
    color: var(--book-fg-muted);
    text-decoration: none;
    border-left: 0.125rem solid transparent;
    border-radius: 0 var(--book-radius) var(--book-radius) 0;
    transition: color var(--book-transition), border-color var(--book-transition), background-color var(--book-transition);
}
.book-outline-list a:hover {
    color: var(--book-fg);
    background: var(--book-accent-soft);
}
.book-outline-list li[data-active="true"] > a {
    color: var(--book-accent);
    border-left-color: var(--book-accent);
    background: var(--book-accent-soft);
    font-weight: 600;
}

/* -----------------------------------------------------------
 * 6) Gate region (body content filled by DESIGN-D paywall.js)
 * --------------------------------------------------------- */
.book-gate {
    background: var(--book-surface);
    border: var(--book-border-w) solid var(--book-border);
    border-radius: var(--book-radius-lg);
    padding: 2rem 1.5rem;
    max-width: var(--book-col-max);
    margin: 2rem auto;
    text-align: center;
}
.book-gate-title {
    font-family: var(--book-serif);
    font-size: 1.625rem;
    line-height: 1.25;
    margin: 0 0 1rem;
    color: var(--book-fg);
}
.book-gate-body {
    font-family: var(--book-serif);
    font-size: var(--book-font-body);
    color: var(--book-fg-muted);
    margin: 0 0 1.5rem;
}
.book-gate-actions {
    display: flex;
    flex-wrap: wrap;
    gap: 0.75rem;
    justify-content: center;
}

/* Article state cards (404, 5xx, integrity error) */
.book-state-card {
    background: var(--book-surface);
    border: var(--book-border-w) solid var(--book-border);
    border-radius: var(--book-radius-lg);
    padding: 2rem 1.5rem;
    max-width: var(--book-col-max);
    margin: 2rem auto;
    text-align: center;
    font-family: var(--book-sans);
}
.book-state-card h1 {
    font-family: var(--book-serif);
    font-size: 1.625rem;
    line-height: 1.25;
    margin: 0 0 0.75rem;
}
.book-state-card p {
    color: var(--book-fg-muted);
    margin: 0 0 1.25rem;
}
.book-state-card button,
.book-state-card a {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    padding: 0.625rem 1.25rem;
    min-height: 2.75rem;
    background: var(--book-accent);
    color: #ffffff;
    border: 0;
    border-radius: var(--book-radius);
    font: inherit;
    font-weight: 600;
    text-decoration: none;
    cursor: pointer;
    transition: opacity var(--book-transition), transform var(--book-transition);
}
.book-state-card button:hover,
.book-state-card a:hover {
    opacity: 0.92;
    transform: translateY(-0.0625rem);
}

/* -----------------------------------------------------------
 * 7) Shortcuts dialog
 * --------------------------------------------------------- */
.book-dialog[open] {
    border: 0;
    padding: 0;
    background: transparent;
    color: inherit;
    max-width: 32rem;
    width: 92vw;
    border-radius: var(--book-radius-lg);
}
.book-dialog::backdrop {
    background: rgba(15, 23, 42, 0.55);
    backdrop-filter: blur(0.25rem);
}
.book-dialog-inner {
    background: var(--book-surface-elev);
    border: var(--book-border-w) solid var(--book-border);
    border-radius: var(--book-radius-lg);
    padding: 1.5rem;
    box-shadow: var(--book-shadow);
}
.book-dialog-head {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: 1rem;
}
.book-dialog-title {
    font-family: var(--book-serif);
    font-size: 1.375rem;
    margin: 0;
    color: var(--book-fg);
}
.book-shortcuts-grid {
    display: grid;
    grid-template-columns: auto 1fr;
    gap: 0.5rem 1rem;
    margin: 0;
    font-family: var(--book-sans);
    font-size: 0.9375rem;
    line-height: 1.5;
}
.book-shortcuts-grid dt {
    display: flex;
    gap: 0.25rem;
    align-items: center;
}
.book-shortcuts-grid dd {
    margin: 0;
    color: var(--book-fg-muted);
}

/* Fallback backdrop for non-native dialog */
.book-dialog-backdrop {
    position: fixed;
    inset: 0;
    background: rgba(15, 23, 42, 0.55);
    z-index: 80;
}
.book-dialog-backdrop[hidden] {
    display: none;
}

/* -----------------------------------------------------------
 * 8) Footer + noscript
 * --------------------------------------------------------- */
.book-footer {
    margin-top: 3rem;
    padding: 2rem 1rem;
    background: var(--book-surface);
    border-top: var(--book-border-w) solid var(--book-border);
}
.book-footer-inner {
    max-width: 90rem;
    margin: 0 auto;
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    justify-content: space-between;
    gap: 1rem;
    font-family: var(--book-sans);
    font-size: 0.875rem;
}
.book-footer-copy {
    margin: 0;
    color: var(--book-fg-muted);
}
.book-footer-links {
    list-style: none;
    padding: 0;
    margin: 0;
    display: flex;
    flex-wrap: wrap;
    gap: 1rem;
}
.book-footer-links a {
    color: var(--book-fg-muted);
    text-decoration: none;
    padding: 0.25rem 0.375rem;
    border-radius: 0.25rem;
}
.book-footer-links a:hover {
    color: var(--book-accent);
}

.book-noscript {
    padding: 1rem;
    background: var(--book-accent-soft);
    border: var(--book-border-w) solid var(--book-accent);
    border-radius: var(--book-radius);
    color: var(--book-fg);
    text-align: center;
    margin: 1rem;
    font-family: var(--book-sans);
}

/* -----------------------------------------------------------
 * 9) Responsive (all rem)
 *    - >= 56.25rem: 3-column sticky sidebars
 *    - < 56.25rem: slide-over tree, collapsed outline
 * --------------------------------------------------------- */
@media (min-width: 56.25rem) {
    .book-grid {
        grid-template-columns: var(--book-sidebar-w) minmax(0, 1fr) var(--book-outline-w);
        grid-template-areas: "tree reader outline";
        padding: var(--book-space-5) 1.5rem;
    }
    /* Outline-collapsed state (book-v1.0.2): drop the right column
       entirely so the article reflows to fill the freed space. */
    body[data-outline-collapsed="true"] .book-grid {
        grid-template-columns: var(--book-sidebar-w) minmax(0, 1fr);
        grid-template-areas: "tree reader";
    }
    body[data-outline-collapsed="true"] .book-outline {
        display: none;
    }
    .book-tree {
        position: sticky;
        top: calc(var(--book-header-h) + 4rem);
        transform: none;
        height: calc(100vh - var(--book-header-h) - 6rem);
        width: auto;
        max-width: none;
        background: transparent;
        border-right: 0;
        box-shadow: none;
        padding: 0 0.5rem 0 0;
    }
    .book-tree-close {
        display: none;
    }
    .book-tree-toggle {
        display: none !important;
    }
    .book-outline {
        position: sticky;
        top: calc(var(--book-header-h) + 4rem);
        height: calc(100vh - var(--book-header-h) - 6rem);
        overflow-y: auto;
    }
    .book-article {
        padding: 2.25rem 2rem;
    }
    .book-landing-h1,
    .book-article h1 {
        font-size: 2.5rem;
    }
}

@media (min-width: 80rem) {
    .book-grid {
        grid-template-columns: 17rem minmax(0, 1fr) 13rem;
        padding: var(--book-space-5) 2rem;
    }
    body[data-outline-collapsed="true"] .book-grid {
        grid-template-columns: 17rem minmax(0, 1fr);
    }
}

@media (max-width: 56.2375rem) {
    .book-tree-toggle {
        display: inline-flex;
    }
    .book-outline {
        max-width: var(--book-col-max);
        margin: 1rem auto 0;
    }
    .book-outline-details {
        padding: 0.5rem 0.875rem;
    }
    /* Mobile: existing inline/collapsed behavior — toggle is desktop-only. */
    .book-outline-toggle {
        display: none;
    }
}

@media (max-width: 40rem) {
    .book-toolbar {
        /* book-v1.0.2: 2-cell layout — search wraps to row 2. */
        grid-template-columns: 1fr auto;
        padding: 0.625rem 0.75rem;
        gap: 0.5rem;
    }
    .book-toolbar-search {
        grid-column: 1 / -1;
        grid-row: 2;
    }
    .book-toolbar {
        grid-template-rows: auto auto;
    }
    .book-tier-badge-label {
        display: none;
    }
    .book-tier-badge {
        padding: 0.375rem;
    }
    .book-grid {
        padding: 1rem 0.75rem;
    }
    .book-article {
        padding: 1.25rem 1rem;
    }
    .book-landing-h1,
    .book-article h1 {
        font-size: 1.875rem;
    }
    .book-article h2 {
        font-size: 1.375rem;
    }
    .book-prevnext {
        grid-template-columns: 1fr;
    }
}

/* -----------------------------------------------------------
 * 10) Motion + slow-network fallbacks
 * --------------------------------------------------------- */
@media (prefers-reduced-motion: reduce) {
    *,
    *::before,
    *::after {
        transition: none !important;
        animation: none !important;
        scroll-behavior: auto !important;
    }
    .book-tree {
        transition: none !important;
    }
}

html[data-motion="reduced"] .book-tree {
    transition: none;
}

html[data-net="slow"] .book-tree-skel {
    animation: none;
    background: var(--book-surface-elev);
}

/* -----------------------------------------------------------
 * 11) In-page search highlight + live cursor (used by search.js)
 * --------------------------------------------------------- */
.book-article mark.book-hit {
    background: color-mix(in oklab, var(--book-tier-paid) 35%, transparent);
    color: inherit;
    padding: 0 0.1875rem;
    border-radius: 0.1875rem;
}

/* -----------------------------------------------------------
 * 12) Print (optional niceties — doesn't eat budget)
 * --------------------------------------------------------- */
@media print {
    .book-toolbar,
    .book-tree,
    .book-outline,
    .book-prevnext,
    .book-footer,
    .book-skiplink,
    .book-shared-header {
        display: none !important;
    }
    .book-grid {
        grid-template-columns: 1fr;
        padding: 0;
    }
    .book-article {
        border: 0;
        padding: 0;
        max-width: none;
    }
    body {
        background: #ffffff;
        color: #000000;
    }
}