/* Learning Resource Hub browse page: fixed sidebar (subject > area > topic tree,
   filters, tags) beside an AJAX result grid. Mirrors Book Explorer's layout and
   uses the same site tokens; result cards come from course_explorer.css. */

.cb-layout {
    display: flex;
    min-height: 100vh;
}

.cb-sidebar {
    position: fixed;
    left: 0;
    top: 0;
    width: 320px;
    height: 100vh;
    background: var(--secondary-dark);
    border-right: 1px solid var(--hairline);
    color: var(--text-primary);
    padding: 1.5rem 1.2rem;
    overflow-y: auto;
    z-index: 100;
    box-sizing: border-box;
}

.cb-sidebar-header {
    margin-bottom: 1rem;
    padding-bottom: 1rem;
    border-bottom: 1px solid var(--hairline);
}

.cb-title-link { text-decoration: none; display: inline-block; }
.cb-title-link:hover .cb-title { opacity: 0.85; }

.cb-title {
    font-size: 1.3rem;
    font-weight: 700;
    margin: 0 0 0.3rem;
    color: var(--text-primary);
}

.cb-subtitle {
    font-size: 0.78rem;
    color: var(--text-secondary);
    margin: 0;
}

.cb-search {
    display: flex;
    gap: 0.5rem;
    margin: 0 0 0.9rem;
}

.cb-search input {
    flex: 1;
    min-width: 0;
    padding: 0.55rem 0.8rem;
    border-radius: 8px;
    border: 1px solid var(--hairline);
    background: var(--tertiary-dark);
    color: var(--text-primary);
}

.cb-search button {
    padding: 0.55rem 0.9rem;
    border-radius: 8px;
    border: 1px solid var(--accent-blue);
    background: transparent;
    color: var(--accent-blue);
    cursor: pointer;
}

.cb-search button:hover { background: color-mix(in srgb, var(--accent-blue) 12%, transparent); }

.cb-section {
    margin-bottom: 0.4rem;
    border-top: 1px solid var(--hairline);
    padding-top: 0.4rem;
}

.cb-section-toggle {
    display: flex;
    align-items: center;
    justify-content: space-between;
    width: 100%;
    background: none;
    border: none;
    color: var(--text-secondary);
    font-size: 0.75rem;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.06em;
    padding: 0.4rem 0.1rem;
    cursor: pointer;
}

.cb-section-toggle:hover { color: var(--text-primary); }
.cb-section-toggle::after { content: '\25B8'; transition: transform 0.15s ease; }
.cb-section-toggle[aria-expanded="true"]::after { transform: rotate(90deg); }

.cb-hint {
    font-size: 0.78rem;
    line-height: 1.35;
    color: var(--text-secondary);
    margin: 0.2rem 0 0;
}

/* ---- Tree ---- */

.cb-tree {
    display: flex;
    flex-direction: column;
    gap: 0.15rem;
    padding-top: 0.35rem;
}

.cb-group-header { display: flex; align-items: stretch; gap: 0.2rem; }

.cb-load {
    flex: 1;
    min-width: 0;
    display: flex;
    justify-content: space-between;
    gap: 0.5rem;
    text-align: left;
    background: none;
    border: none;
    border-radius: 6px;
    color: var(--text-secondary);
    padding: 0.4rem 0.4rem;
    font-size: 0.84rem;
    cursor: pointer;
}

.cb-load:hover {
    background: color-mix(in srgb, var(--accent-blue) 8%, transparent);
    color: var(--text-primary);
}

.cb-load.active { color: var(--accent-blue); font-weight: 700; }

.cb-count {
    font-size: 0.68rem;
    color: var(--text-muted);
    margin-left: 0.3rem;
    font-variant-numeric: tabular-nums;
}

.cb-expand {
    flex-shrink: 0;
    background: none;
    border: none;
    border-radius: 6px;
    color: var(--text-muted);
    padding: 0.4rem 0.5rem;
    cursor: pointer;
}

.cb-expand:hover { background: color-mix(in srgb, var(--accent-blue) 8%, transparent); }
.cb-chevron { display: inline-block; font-size: 0.7rem; transition: transform 0.15s ease; }
.cb-expand[aria-expanded="true"] .cb-chevron { transform: rotate(90deg); }

.cb-list {
    display: flex;
    flex-direction: column;
    gap: 0.1rem;
    padding: 0.1rem 0 0.4rem 0.8rem;
}

.cb-list[hidden] { display: none; }

.cb-area-plain { padding-right: 1.9rem; }

.cb-leaves {
    flex-direction: row;
    flex-wrap: wrap;
    gap: 0.3rem;
    padding: 0.2rem 0 0.5rem 0.9rem;
}

.cb-chip {
    display: inline-flex;
    align-items: center;
    padding: 0.28rem 0.65rem;
    border-radius: 14px;
    border: 1px solid var(--hairline);
    background: var(--tertiary-dark);
    color: var(--text-secondary);
    font-size: 0.76rem;
    cursor: pointer;
    text-align: left;
}

.cb-chip:hover { border-color: var(--accent-blue); color: var(--text-primary); }

.cb-chip.active {
    background: color-mix(in srgb, var(--accent-blue) 14%, transparent);
    border-color: var(--accent-blue);
    color: var(--text-primary);
    font-weight: 600;
}

/* ---- Filters ---- */

.cb-filter-group { margin: 0.5rem 0 0.9rem; }

.cb-filter-group h3 {
    font-size: 0.72rem;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--text-secondary);
    margin: 0 0 0.4rem;
    font-weight: 700;
}

.cb-filter-group select {
    width: 100%;
    padding: 0.4rem 0.5rem;
    border-radius: 6px;
    border: 1px solid var(--hairline);
    background: var(--tertiary-dark);
    color: var(--text-primary);
}

.cb-chips { display: flex; flex-wrap: wrap; gap: 0.35rem; }

.cb-clear,
.cb-clear-search {
    background: none;
    border: none;
    color: var(--accent-blue);
    font-size: 0.8rem;
    text-decoration: underline;
    cursor: pointer;
    padding: 0.2rem 0;
}

.cb-clear { margin-top: 0.4rem; }

/* ---- Extras ---- */

.cb-extras { padding-top: 0.8rem; }

.cb-saved {
    display: block;
    margin-bottom: 0.6rem;
    font-size: 0.85rem;
    color: var(--accent-blue);
    text-decoration: none;
}

.cb-saved:hover { text-decoration: underline; }

.cb-suggest summary {
    cursor: pointer;
    font-size: 0.82rem;
    color: var(--text-secondary);
}

.cb-suggest summary:hover { color: var(--text-primary); }

.cb-suggest-form {
    display: flex;
    flex-direction: column;
    gap: 0.4rem;
    margin-top: 0.5rem;
}

.cb-suggest-form input,
.cb-suggest-form select {
    padding: 0.4rem 0.6rem;
    border-radius: 6px;
    border: 1px solid var(--hairline);
    background: var(--tertiary-dark);
    color: var(--text-primary);
    font-size: 0.82rem;
}

.cb-suggest-form button {
    align-self: flex-start;
    padding: 0.4rem 0.9rem;
    border-radius: 8px;
    border: 1px solid var(--accent-blue);
    background: transparent;
    color: var(--accent-blue);
    cursor: pointer;
}

.cb-suggest-form button:disabled { opacity: 0.6; cursor: default; }

/* ---- Results pane ---- */

.cb-main {
    margin-left: 320px;
    flex: 1;
    padding: 1.75rem 2rem 4rem;
    min-width: 0;
}

.cb-header { margin-bottom: 1.2rem; }

.cb-crumbs {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    gap: 0.25rem;
    font-size: 0.85rem;
    color: var(--text-muted);
    margin-bottom: 0.4rem;
}

.cb-crumbs[hidden] { display: none; }

.cb-crumbs button {
    background: none;
    border: none;
    padding: 0.1rem 0.2rem;
    color: var(--accent-blue);
    font-size: inherit;
    cursor: pointer;
}

.cb-crumbs button:hover { text-decoration: underline; }

.cb-page-title {
    font-size: 1.6rem;
    font-weight: 700;
    color: var(--text-primary);
    margin: 0 0 0.25rem;
}

.cb-scope { font-size: 1rem; font-weight: 500; color: var(--text-secondary); }

.cb-result-count { font-size: 0.85rem; color: var(--text-secondary); margin: 0; }

.cb-clear-search[hidden] { display: none; }

#cb-grid[aria-busy="true"] { opacity: 0.45; transition: opacity 0.15s ease; }

.cb-load-more {
    display: block;
    margin: 2rem auto 0;
    padding: 0.6rem 1.5rem;
    border-radius: 20px;
    border: 1px solid var(--accent-blue);
    background: transparent;
    color: var(--accent-blue);
    cursor: pointer;
}

.cb-load-more:hover { background: color-mix(in srgb, var(--accent-blue) 12%, transparent); }
.cb-load-more[hidden] { display: none; }

.cb-empty {
    grid-column: 1 / -1;
    text-align: center;
    padding: 3rem 1rem;
    color: var(--text-secondary);
}

.cb-empty-icon { font-size: 3rem; margin-bottom: 0.5rem; }

.cb-sidebar :focus-visible,
.cb-main :focus-visible {
    outline: 2px solid var(--accent-blue);
    outline-offset: 2px;
    border-radius: 4px;
}

@media (max-width: 900px) {
    /* touch targets */
    .cb-load, .cb-expand { min-height: 42px; align-items: center; }
    .cb-chip { min-height: 36px; }
    .cb-search input, .cb-search button, .cb-filter-group select { min-height: 42px; }
    .cb-layout { flex-direction: column; }
    .cb-sidebar { position: relative; width: 100%; height: auto; }
    .cb-main { margin-left: 0; padding: 1.25rem 1rem 3rem; }
}

@media (prefers-reduced-motion: reduce) {
    .cb-chevron, .cb-section-toggle::after, #cb-grid[aria-busy="true"] { transition: none; }
}