/* =============================================
   Research Hub - Clean & Readable Design
   ============================================= */

/* --- Reset & Base --- */
*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

:root {
    --color-bg: #fafafa;
    --color-surface: #ffffff;
    --color-text: #1a1a2e;
    --color-text-secondary: #555770;
    --color-text-muted: #8888a0;
    --color-border: #e2e2ec;
    --color-accent: #2563eb;
    --color-accent-light: #eff4ff;
    --color-accent-hover: #1d4ed8;
    --color-category: #059669;
    --color-category-bg: #ecfdf5;
    --color-code-bg: #f4f4f8;
    --font-sans: 'Inter', 'Noto Sans JP', -apple-system, BlinkMacSystemFont, sans-serif;
    --font-mono: 'JetBrains Mono', 'Fira Code', monospace;
    --max-width: 1100px;
    --sidebar-width: 260px;
    --radius: 8px;
    --shadow-sm: 0 1px 3px rgba(0,0,0,0.06);
    --shadow-md: 0 4px 12px rgba(0,0,0,0.08);
}

html {
    font-size: 16px;
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-sans);
    color: var(--color-text);
    background: var(--color-bg);
    line-height: 1.7;
    -webkit-font-smoothing: antialiased;
}

a {
    color: var(--color-accent);
    text-decoration: none;
    transition: color 0.2s;
}
a:hover {
    color: var(--color-accent-hover);
}

/* --- Header --- */
.site-header {
    background: var(--color-surface);
    border-bottom: 1px solid var(--color-border);
    position: sticky;
    top: 0;
    z-index: 100;
}

.header-inner {
    max-width: var(--max-width);
    margin: 0 auto;
    padding: 0.75rem 1.5rem;
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.site-logo {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    color: var(--color-text);
    text-decoration: none;
}

.logo-icon {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 40px;
    height: 40px;
    background: var(--color-accent);
    color: #fff;
    border-radius: var(--radius);
    font-weight: 700;
    font-size: 1.25rem;
}

.logo-title {
    display: block;
    font-weight: 700;
    font-size: 1.1rem;
    letter-spacing: -0.02em;
}

.logo-subtitle {
    display: block;
    font-size: 0.72rem;
    color: var(--color-text-muted);
    font-weight: 400;
}

.site-nav {
    display: flex;
    gap: 2rem;
}

.site-nav a {
    color: var(--color-text-secondary);
    font-size: 0.9rem;
    font-weight: 500;
    padding: 0.25rem 0;
    border-bottom: 2px solid transparent;
    transition: color 0.2s, border-color 0.2s;
}

.site-nav a:hover {
    color: var(--color-accent);
    border-bottom-color: var(--color-accent);
}

.nav-toggle {
    display: none;
    background: none;
    border: none;
    cursor: pointer;
    padding: 0.5rem;
    flex-direction: column;
    gap: 5px;
}
.nav-toggle span {
    display: block;
    width: 22px;
    height: 2px;
    background: var(--color-text);
    border-radius: 2px;
    transition: 0.2s;
}

/* --- Layout --- */
.site-main {
    max-width: var(--max-width);
    margin: 0 auto;
    padding: 2rem 1.5rem;
    min-height: calc(100vh - 200px);
}

.page-layout {
    display: grid;
    grid-template-columns: 1fr var(--sidebar-width);
    gap: 3rem;
    align-items: start;
}

/* --- Page Header --- */
.page-header {
    margin-bottom: 2rem;
}

.page-title {
    font-size: 1.75rem;
    font-weight: 700;
    letter-spacing: -0.02em;
    color: var(--color-text);
}

.page-desc {
    margin-top: 0.5rem;
    color: var(--color-text-secondary);
    font-size: 0.95rem;
}

.back-link {
    display: inline-block;
    margin-top: 0.75rem;
    font-size: 0.85rem;
    color: var(--color-text-muted);
}
.back-link:hover {
    color: var(--color-accent);
}

/* --- Article Cards --- */
.article-list {
    display: flex;
    flex-direction: column;
    gap: 1px;
}

.article-card {
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius);
    padding: 1.5rem 1.75rem;
    transition: box-shadow 0.2s, border-color 0.2s;
    margin-bottom: 1rem;
}

.article-card:hover {
    box-shadow: var(--shadow-md);
    border-color: #ccc;
}

.card-category a {
    display: inline-block;
    font-size: 0.75rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.04em;
    color: var(--color-category);
    background: var(--color-category-bg);
    padding: 0.15rem 0.6rem;
    border-radius: 4px;
}

.card-title {
    font-size: 1.2rem;
    font-weight: 600;
    margin-top: 0.6rem;
    line-height: 1.4;
}

.card-title a {
    color: var(--color-text);
}
.card-title a:hover {
    color: var(--color-accent);
}

.card-summary {
    margin-top: 0.5rem;
    color: var(--color-text-secondary);
    font-size: 0.9rem;
    line-height: 1.6;
}

.card-meta {
    margin-top: 0.75rem;
    display: flex;
    align-items: center;
    gap: 1rem;
    flex-wrap: wrap;
}

.card-meta time {
    font-size: 0.8rem;
    color: var(--color-text-muted);
}

.card-tags {
    display: flex;
    gap: 0.4rem;
    flex-wrap: wrap;
}

.tag {
    font-size: 0.72rem;
    color: var(--color-text-muted);
    background: var(--color-code-bg);
    padding: 0.1rem 0.5rem;
    border-radius: 3px;
}

/* --- Sidebar --- */
.sidebar {
    position: sticky;
    top: 5rem;
}

.sidebar-section {
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius);
    padding: 1.25rem;
    margin-bottom: 1rem;
}

.sidebar-title {
    font-size: 0.8rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.06em;
    color: var(--color-text-muted);
    margin-bottom: 0.75rem;
}

.category-list {
    list-style: none;
}

.category-list li {
    border-radius: 6px;
}

.category-list li a {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0.45rem 0.6rem;
    font-size: 0.88rem;
    color: var(--color-text-secondary);
    border-radius: 6px;
    transition: background 0.15s, color 0.15s;
}

.category-list li a:hover {
    background: var(--color-accent-light);
    color: var(--color-accent);
}

.category-list li.active a {
    background: var(--color-accent-light);
    color: var(--color-accent);
    font-weight: 500;
}

.category-list .count {
    font-size: 0.75rem;
    background: var(--color-code-bg);
    padding: 0.1rem 0.45rem;
    border-radius: 10px;
    color: var(--color-text-muted);
}

/* --- Sidebar Series Quick Nav --- */
.series-quick-list {
    list-style: none;
}

.series-quick-list li a {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    gap: 0.5rem;
    padding: 0.5rem 0.6rem;
    font-size: 0.82rem;
    color: var(--color-text-secondary);
    border-radius: 6px;
    transition: background 0.15s, color 0.15s;
    line-height: 1.4;
}

.series-quick-list li a:hover {
    background: var(--color-accent-light);
    color: var(--color-accent);
}

.series-quick-name {
    flex: 1;
    display: -webkit-box;
    -webkit-line-clamp: 2;
    -webkit-box-orient: vertical;
    overflow: hidden;
}

/* =============================================
   Series Block (Index Page) - Collapsible
   ============================================= */
.series-block {
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius);
    margin-bottom: 1.25rem;
    transition: box-shadow 0.25s, border-color 0.25s;
    overflow: hidden;
}

.series-block:hover {
    box-shadow: var(--shadow-md);
    border-color: #ccd;
}

.series-block.expanded {
    border-color: var(--color-accent);
    box-shadow: 0 2px 16px rgba(37, 99, 235, 0.1);
}

/* --- Series Header (clickable) --- */
.series-header {
    padding: 1.5rem 1.75rem;
    cursor: pointer;
    position: relative;
    user-select: none;
    transition: background 0.15s;
}

.series-header:hover {
    background: #fafaff;
}

.series-header-top {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 0.6rem;
}

.series-badges {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    flex-wrap: wrap;
}

.series-badge {
    display: inline-block;
    font-size: 0.68rem;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.06em;
    color: #fff;
    background: var(--color-accent);
    padding: 0.2rem 0.6rem;
    border-radius: 4px;
}

.series-parts-badge {
    font-size: 0.72rem;
    font-weight: 600;
    color: var(--color-accent);
    background: var(--color-accent-light);
    padding: 0.15rem 0.55rem;
    border-radius: 4px;
}

.series-toggle-icon {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 32px;
    height: 32px;
    border-radius: 50%;
    color: var(--color-text-muted);
    transition: transform 0.3s ease, background 0.2s, color 0.2s;
    flex-shrink: 0;
}

.series-block.expanded .series-toggle-icon {
    transform: rotate(180deg);
    color: var(--color-accent);
    background: var(--color-accent-light);
}

.series-title {
    font-size: 1.15rem;
    font-weight: 700;
    color: var(--color-text);
    line-height: 1.4;
    margin-bottom: 0.4rem;
}

.series-overview-summary {
    font-size: 0.88rem;
    color: var(--color-text-secondary);
    line-height: 1.6;
    margin-bottom: 0.6rem;
}

.series-header-meta {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    flex-wrap: wrap;
}

.series-header-meta time {
    font-size: 0.78rem;
    color: var(--color-text-muted);
}

.card-category-inline a {
    font-size: 0.72rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.04em;
    color: var(--color-category);
    background: var(--color-category-bg);
    padding: 0.1rem 0.5rem;
    border-radius: 4px;
}

/* --- Series TOC (collapsible) --- */
.series-toc-wrapper {
    max-height: 0;
    overflow: hidden;
    transition: max-height 0.35s ease;
}

.series-block.expanded .series-toc-wrapper {
    max-height: 1200px;
}

.series-toc {
    list-style: none;
    margin: 0;
    padding: 0 1.75rem 1.25rem;
    border-top: 1px solid var(--color-border);
}

.series-toc li {
    border-bottom: 1px solid #f0f0f5;
}

.series-toc li:last-child {
    border-bottom: none;
}

.series-toc-item {
    display: flex;
    align-items: center;
    gap: 0.85rem;
    padding: 0.7rem 0.5rem;
    color: var(--color-text);
    text-decoration: none;
    border-radius: 6px;
    transition: background 0.15s, transform 0.15s;
}

.series-toc-item:hover {
    background: var(--color-accent-light);
    color: var(--color-accent);
    transform: translateX(4px);
}

.series-toc-number {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 28px;
    height: 28px;
    border-radius: 50%;
    background: var(--color-code-bg);
    color: var(--color-text-muted);
    font-size: 0.72rem;
    font-weight: 700;
    font-family: var(--font-mono);
    flex-shrink: 0;
    transition: background 0.15s, color 0.15s;
}

.series-toc-item:hover .series-toc-number {
    background: var(--color-accent);
    color: #fff;
}

.series-toc-content {
    flex: 1;
    min-width: 0;
}

.series-toc-title {
    display: block;
    font-size: 0.92rem;
    font-weight: 500;
    line-height: 1.4;
}

.series-toc-label {
    display: block;
    font-size: 0.72rem;
    color: var(--color-text-muted);
    margin-top: 0.1rem;
}

.series-toc-arrow {
    color: var(--color-text-muted);
    font-size: 0.85rem;
    opacity: 0;
    transition: opacity 0.15s, transform 0.15s;
    flex-shrink: 0;
}

.series-toc-item:hover .series-toc-arrow {
    opacity: 1;
    transform: translateX(2px);
}

/* =============================================
   Article Full View
   ============================================= */
.article-full {
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius);
    padding: 2.5rem;
}

.article-header {
    margin-bottom: 2rem;
    padding-bottom: 1.5rem;
    border-bottom: 1px solid var(--color-border);
}

.article-category {
    display: inline-block;
    font-size: 0.75rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.04em;
    color: var(--color-category);
    background: var(--color-category-bg);
    padding: 0.15rem 0.6rem;
    border-radius: 4px;
}

.article-title {
    font-size: 1.75rem;
    font-weight: 700;
    margin-top: 0.75rem;
    line-height: 1.35;
    letter-spacing: -0.02em;
}

.article-meta {
    margin-top: 0.75rem;
    display: flex;
    align-items: center;
    gap: 1rem;
    flex-wrap: wrap;
}

.article-meta time {
    font-size: 0.85rem;
    color: var(--color-text-muted);
}

.article-tags {
    display: flex;
    gap: 0.4rem;
}

.article-footer {
    margin-top: 3rem;
    padding-top: 1.5rem;
    border-top: 1px solid var(--color-border);
}

/* --- Series Nav in Article --- */
.article-series-badge {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    margin-top: 0.5rem;
    flex-wrap: wrap;
}

.article-series-badge .series-name {
    font-size: 0.85rem;
    font-weight: 500;
    color: var(--color-text-secondary);
}

.article-series-badge .series-part {
    font-size: 0.78rem;
    color: var(--color-text-muted);
}

.series-nav-toc {
    background: var(--color-bg);
    border: 1px solid var(--color-border);
    border-radius: var(--radius);
    padding: 1.25rem 1.5rem;
    margin-bottom: 2rem;
}

.series-nav-toc-title {
    font-size: 0.8rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.04em;
    color: var(--color-text-muted);
    margin-bottom: 0.6rem;
}

.series-nav-toc-list {
    list-style: none;
    margin: 0;
    padding: 0;
    counter-reset: toc-counter;
}

.series-nav-toc-list li {
    counter-increment: toc-counter;
    padding: 0.3rem 0;
    font-size: 0.88rem;
}

.series-nav-toc-list li a {
    color: var(--color-text-secondary);
    transition: color 0.15s;
}

.series-nav-toc-list li a:hover {
    color: var(--color-accent);
}

.series-nav-toc-list li.current {
    font-weight: 600;
    color: var(--color-accent);
}

.series-nav-toc-list li.current .series-nav-current {
    color: var(--color-accent);
    border-left: 3px solid var(--color-accent);
    padding-left: 0.5rem;
    margin-left: -0.5rem;
}

/* --- Series Pager (Prev/Next) --- */
.series-pager {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 1rem;
    margin-top: 2.5rem;
    padding-top: 1.5rem;
    border-top: 1px solid var(--color-border);
}

.series-pager a {
    display: block;
    padding: 1rem;
    border: 1px solid var(--color-border);
    border-radius: var(--radius);
    text-decoration: none;
    transition: border-color 0.2s, box-shadow 0.2s;
}

.series-pager a:hover {
    border-color: var(--color-accent);
    box-shadow: var(--shadow-sm);
}

.pager-prev { text-align: left; }
.pager-next { text-align: right; }

.pager-direction {
    display: block;
    font-size: 0.75rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.04em;
    color: var(--color-accent);
    margin-bottom: 0.3rem;
}

.pager-label {
    display: block;
    font-size: 0.72rem;
    color: var(--color-text-muted);
}

.pager-title {
    display: block;
    font-size: 0.9rem;
    font-weight: 500;
    color: var(--color-text);
    line-height: 1.4;
    margin-top: 0.15rem;
}

/* =============================================
   Prose (Article Body)
   ============================================= */
.prose h1 { font-size: 1.6rem; margin: 2rem 0 1rem; font-weight: 700; letter-spacing: -0.01em; }
.prose h2 { font-size: 1.35rem; margin: 1.8rem 0 0.8rem; font-weight: 600; letter-spacing: -0.01em; }
.prose h3 { font-size: 1.1rem; margin: 1.5rem 0 0.6rem; font-weight: 600; }
.prose h4 { font-size: 1rem; margin: 1.2rem 0 0.5rem; font-weight: 600; }

.prose p {
    margin-bottom: 1.1rem;
    line-height: 1.8;
}

.prose ul, .prose ol {
    margin: 0.8rem 0 1.1rem 1.5rem;
}
.prose li {
    margin-bottom: 0.35rem;
    line-height: 1.7;
}

.prose blockquote {
    margin: 1.2rem 0;
    padding: 0.8rem 1.2rem;
    border-left: 3px solid var(--color-accent);
    background: var(--color-accent-light);
    color: var(--color-text-secondary);
    border-radius: 0 var(--radius) var(--radius) 0;
}

.prose code {
    font-family: var(--font-mono);
    font-size: 0.88em;
    background: var(--color-code-bg);
    padding: 0.15em 0.4em;
    border-radius: 4px;
    color: #c7254e;
}

.prose pre {
    margin: 1.2rem 0;
    padding: 1.2rem 1.5rem;
    background: #1e1e2e;
    color: #cdd6f4;
    border-radius: var(--radius);
    overflow-x: auto;
    font-size: 0.85rem;
    line-height: 1.6;
}

.prose pre code {
    background: none;
    padding: 0;
    color: inherit;
    font-size: inherit;
}

.prose table {
    width: 100%;
    margin: 1.2rem 0;
    border-collapse: collapse;
}

.prose th, .prose td {
    padding: 0.6rem 1rem;
    border: 1px solid var(--color-border);
    text-align: left;
    font-size: 0.9rem;
}

.prose th {
    background: var(--color-code-bg);
    font-weight: 600;
}

.prose img {
    max-width: 100%;
    height: auto;
    border-radius: var(--radius);
    margin: 1rem 0;
}

.prose hr {
    border: none;
    border-top: 1px solid var(--color-border);
    margin: 2rem 0;
}

.prose .highlight {
    margin: 1.2rem 0;
    border-radius: var(--radius);
    overflow-x: auto;
}
.prose .highlight pre {
    margin: 0;
}

/* --- About Page --- */
.about-page .prose {
    max-width: 700px;
}

.research-areas {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 1.25rem;
    margin: 1.5rem 0;
}

.research-card {
    background: var(--color-bg);
    border: 1px solid var(--color-border);
    border-radius: var(--radius);
    padding: 1.5rem;
    transition: box-shadow 0.2s;
}

.research-card:hover {
    box-shadow: var(--shadow-md);
}

.research-icon {
    font-size: 2rem;
    margin-bottom: 0.5rem;
}

.research-card h3 {
    font-size: 1rem;
    font-weight: 600;
    margin-bottom: 0.5rem;
}

.research-card p {
    font-size: 0.88rem;
    color: var(--color-text-secondary);
    line-height: 1.6;
}

/* --- Empty State --- */
.empty-state {
    text-align: center;
    padding: 4rem 2rem;
    color: var(--color-text-muted);
}

/* --- Footer --- */
.site-footer {
    border-top: 1px solid var(--color-border);
    margin-top: 4rem;
}

.footer-inner {
    max-width: var(--max-width);
    margin: 0 auto;
    padding: 1.5rem;
    text-align: center;
    font-size: 0.8rem;
    color: var(--color-text-muted);
}

/* =============================================
   Responsive
   ============================================= */
@media (max-width: 768px) {
    .page-layout {
        grid-template-columns: 1fr;
        gap: 1.5rem;
    }

    .sidebar {
        position: static;
        order: -1;
    }

    .sidebar-section {
        padding: 1rem;
    }

    .category-list {
        display: flex;
        flex-wrap: wrap;
        gap: 0.3rem;
    }

    .category-list li a {
        padding: 0.3rem 0.6rem;
        font-size: 0.82rem;
    }

    .series-quick-list {
        display: flex;
        flex-wrap: wrap;
        gap: 0.3rem;
    }

    .series-quick-list li a {
        padding: 0.3rem 0.6rem;
        font-size: 0.78rem;
    }

    .site-nav {
        display: none;
        position: absolute;
        top: 100%;
        left: 0;
        right: 0;
        background: var(--color-surface);
        border-bottom: 1px solid var(--color-border);
        flex-direction: column;
        padding: 1rem 1.5rem;
        gap: 0.75rem;
    }

    .site-nav.open {
        display: flex;
    }

    .nav-toggle {
        display: flex;
    }

    .article-full {
        padding: 1.5rem;
    }

    .article-title {
        font-size: 1.4rem;
    }

    .research-areas {
        grid-template-columns: 1fr;
    }

    .header-inner {
        padding: 0.75rem 1rem;
    }

    .site-main {
        padding: 1.5rem 1rem;
    }

    .series-pager {
        grid-template-columns: 1fr;
    }

    .series-header {
        padding: 1.25rem;
    }

    .series-toc {
        padding: 0 1.25rem 1rem;
    }

    .series-title {
        font-size: 1rem;
    }
}