/* === RESET & BASE === */
*, *::before, *::after {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root {
    --abyssal-navy: #0a2942;
    --deep-reading: #1e3a54;
    --teal-ocean: #2d6a8a;
    --mid-ocean: #4a7a9b;
    --seafoam-glow: #00e5c8;
    --bioluminescent: #00b4d8;
    --parchment: #f4f0eb;
    --aged-linen: #e8e2d8;
    --wabi-rust: #c47a5a;
    --deep-ink: #1a3a5c;
    --margin-parchment: #ddd6ca;
}

html {
    scroll-behavior: smooth;
}

body {
    background-color: var(--aged-linen);
    color: var(--deep-reading);
    font-family: 'Source Serif 4', Georgia, serif;
    font-size: clamp(0.95rem, 1.1vw, 1.1rem);
    font-weight: 400;
    line-height: 1.72;
    letter-spacing: 0.005em;
}

/* === HEADER === */
.site-header {
    text-align: center;
    padding: 48px 24px 0;
    border-bottom: 1px solid var(--abyssal-navy);
    position: relative;
    overflow: hidden;
}

.site-title {
    font-family: 'Nunito', sans-serif;
    font-size: clamp(1.8rem, 4vw, 3.2rem);
    font-weight: 800;
    letter-spacing: -0.01em;
    color: var(--abyssal-navy);
    opacity: 0;
    animation: fade-in 1.2s ease forwards;
}

.site-subtitle {
    font-family: 'Source Serif 4', Georgia, serif;
    font-size: clamp(0.9rem, 1.2vw, 1.05rem);
    color: var(--mid-ocean);
    font-style: italic;
    margin-top: 8px;
    min-height: 1.5em;
}

.site-subtitle .char {
    opacity: 0;
    animation: char-appear 0.05s ease forwards;
}

@keyframes char-appear {
    to { opacity: 1; }
}

@keyframes fade-in {
    to { opacity: 1; }
}

/* === WAVE === */
.wave-container {
    width: 100%;
    height: 40px;
    overflow: hidden;
    margin-top: 16px;
}

.wave-svg {
    width: 200%;
    height: 100%;
    animation: wave-drift 25s linear infinite;
}

@keyframes wave-drift {
    from { transform: translateX(0); }
    to { transform: translateX(-50%); }
}

/* === TOPIC NAV === */
.topic-nav {
    display: flex;
    gap: 10px;
    padding: 20px 24px;
    max-width: 1400px;
    margin: 0 auto;
    overflow-x: auto;
    -webkit-overflow-scrolling: touch;
    scrollbar-width: none;
}

.topic-nav::-webkit-scrollbar {
    display: none;
}

.topic-pill {
    font-family: 'Nunito Sans', sans-serif;
    font-size: 0.78rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    color: var(--mid-ocean);
    background: transparent;
    border: 1.5px solid var(--mid-ocean);
    border-radius: 20px;
    padding: 6px 18px;
    cursor: pointer;
    white-space: nowrap;
    transition: all 0.25s ease;
    opacity: 0;
    transform: translateY(20px);
}

.topic-pill.visible {
    opacity: 1;
    transform: translateY(0);
}

.topic-pill:hover {
    color: var(--abyssal-navy);
    border-color: var(--abyssal-navy);
}

.topic-pill.active {
    color: var(--abyssal-navy);
    border-color: var(--seafoam-glow);
    border-bottom-width: 3px;
    text-shadow: 0 0 8px rgba(0, 229, 200, 0.25);
}

/* === CARD GRID === */
.card-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
    gap: 24px;
    max-width: 1400px;
    width: 90%;
    margin: 12px auto 60px;
    padding: 0 12px;
}

/* === KNOWLEDGE CARD === */
.knowledge-card {
    position: relative;
    background: var(--parchment);
    border-radius: 12px 14px 11px 13px;
    border: 2px solid var(--deep-ink);
    overflow: hidden;
    cursor: pointer;
    opacity: 0;
    transform: translateY(30px);
    transition: opacity 0.5s ease-out, transform 0.5s ease-out, box-shadow 0.2s ease, border-color 0.4s ease;
    /* paper texture via gradient spots */
    background-image:
        radial-gradient(ellipse at 20% 30%, rgba(10,41,66,0.03) 0%, transparent 50%),
        radial-gradient(ellipse at 70% 60%, rgba(196,122,90,0.025) 0%, transparent 40%),
        radial-gradient(ellipse at 50% 80%, rgba(10,41,66,0.02) 0%, transparent 60%);
    background-color: var(--parchment);
}

.knowledge-card.visible {
    opacity: 1;
    transform: rotate(var(--rotation, 0deg));
}

.knowledge-card:hover {
    transform: translateY(-4px) rotate(var(--rotation, 0deg));
    box-shadow: 0 8px 24px rgba(10, 41, 66, 0.12);
}

.knowledge-card.expanded {
    grid-column: 1 / -1;
    border-color: var(--bioluminescent);
    animation: pulse-glow 2s ease-in-out infinite;
    transform: rotate(0deg);
}

.knowledge-card.expanded:hover {
    transform: rotate(0deg);
}

@keyframes pulse-glow {
    0%, 100% { box-shadow: 0 0 10px rgba(0, 180, 216, 0.15); }
    50% { box-shadow: 0 0 25px rgba(0, 180, 216, 0.3); }
}

/* Feature card spans 2 columns */
.feature-card {
    grid-column: span 2;
}

@media (max-width: 768px) {
    .feature-card {
        grid-column: span 1;
    }
}

/* === PAGE FOLD CORNER === */
.card-fold {
    position: absolute;
    top: 0;
    right: 0;
    width: 28px;
    height: 28px;
    background: var(--aged-linen);
    clip-path: polygon(0 0, 100% 0, 100% 100%);
    z-index: 2;
    transition: width 0.4s ease, height 0.4s ease, background 0.4s ease;
}

.knowledge-card:hover .card-fold {
    width: 40px;
    height: 40px;
    background: var(--teal-ocean);
}

/* === BOOKMARK RIBBON === */
.bookmark-ribbon {
    position: absolute;
    top: 0;
    left: 20px;
    width: 3px;
    height: 36px;
    background: var(--wabi-rust);
    z-index: 2;
    border-radius: 0 0 1px 1px;
}

/* === CARD MARGIN === */
.card-margin {
    position: absolute;
    top: 0;
    left: 0;
    width: 40px;
    height: 100%;
    background: var(--margin-parchment);
    display: flex;
    flex-direction: column;
    align-items: center;
    padding-top: 40px;
    gap: 12px;
    border-right: 1px solid rgba(10, 41, 66, 0.08);
}

.margin-mark {
    font-family: 'Fira Code', monospace;
    font-size: 0.6rem;
    color: var(--wabi-rust);
    opacity: 0.5;
}

.knowledge-card:has(.card-margin) .card-content {
    margin-left: 40px;
}

/* === CARD CONTENT === */
.card-content {
    padding: 20px 24px 24px;
}

.card-meta {
    font-family: 'Nunito Sans', sans-serif;
    font-size: 0.78rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    color: var(--mid-ocean);
    display: block;
    margin-bottom: 8px;
}

.card-title {
    font-family: 'Nunito', sans-serif;
    font-size: clamp(1.1rem, 2vw, 1.4rem);
    font-weight: 800;
    letter-spacing: -0.01em;
    color: var(--abyssal-navy);
    margin-bottom: 10px;
    line-height: 1.3;
}

.card-body {
    color: var(--deep-reading);
    margin-bottom: 16px;
}

/* === CARD STATS === */
.card-stats {
    display: flex;
    gap: 20px;
    flex-wrap: wrap;
    margin-top: 12px;
}

.stat {
    display: flex;
    flex-direction: column;
    align-items: flex-start;
}

.counter {
    font-family: 'Fira Code', monospace;
    font-size: 1.3rem;
    font-weight: 400;
    color: var(--teal-ocean);
    text-shadow: 0 0 8px rgba(0, 229, 200, 0.35);
}

.stat-label {
    font-family: 'Nunito Sans', sans-serif;
    font-size: 0.7rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.06em;
    color: var(--mid-ocean);
    margin-top: 2px;
}

/* === EXPANDED CONTENT === */
.card-expanded-content {
    display: none;
    margin-top: 20px;
    padding-top: 20px;
    border-top: 1px dashed var(--mid-ocean);
}

.knowledge-card.expanded .card-expanded-content {
    display: block;
    animation: fade-in 0.4s ease forwards;
}

.card-expanded-content p {
    margin-bottom: 14px;
}

/* === FORMULA === */
.formula {
    background: var(--aged-linen);
    padding: 12px 18px;
    border-radius: 6px;
    margin: 16px 0;
    border-left: 3px solid var(--teal-ocean);
}

.formula code {
    font-family: 'Fira Code', monospace;
    font-size: 0.88rem;
    color: var(--teal-ocean);
}

/* === RELATED CONCEPTS === */
.related-concepts {
    display: flex;
    flex-wrap: wrap;
    gap: 8px;
    margin-top: 16px;
}

.related-tag {
    font-family: 'Nunito Sans', sans-serif;
    font-size: 0.72rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.06em;
    color: var(--teal-ocean);
    background: rgba(45, 106, 138, 0.08);
    border: 1px solid rgba(45, 106, 138, 0.2);
    border-radius: 14px;
    padding: 4px 12px;
}

/* === FURTHER READING === */
.further-reading {
    margin-top: 18px;
    padding-top: 12px;
    border-top: 1px solid rgba(10, 41, 66, 0.08);
}

.bib-entry {
    font-size: 0.88rem;
    color: var(--mid-ocean);
    padding-left: 2em;
    text-indent: -2em;
    margin-bottom: 8px;
}

.bib-entry em {
    color: var(--deep-reading);
}

/* === FOOTER === */
.site-footer {
    text-align: center;
    padding: 0 24px 32px;
    max-width: 1400px;
    margin: 0 auto;
}

.footer-wave {
    width: 100%;
    height: 20px;
    margin-bottom: 16px;
}

.footer-text {
    font-family: 'Nunito Sans', sans-serif;
    font-size: 0.78rem;
    font-weight: 600;
    letter-spacing: 0.04em;
    color: var(--mid-ocean);
}

/* === HIDDEN STATE FOR TOPIC FILTER === */
.knowledge-card.hidden-topic {
    display: none;
}