/* ============================================================
   ΕΠΙΣΤΗΜΟΝΙΚΕΣ ΣΗΜΕΙΩΣΕΙΣ — style.css
   Dark academic theme · Greek + LaTeX support
   =========================================================== */

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

/* ── DESIGN TOKENS ────────────────────────────────────────── */
:root {
  /* Background scale */
  --bg:          #0b0c0f;
  --surface:     #11131a;
  --surface-2:   #171a23;
  --surface-3:   #1e2130;

  /* Borders */
  --border:      #1f2333;
  --border-2:    #2a2f44;
  --border-3:    #363d58;

  /* Text scale */
  --text:        #dde1ee;
  --text-mid:    #8a92b2;
  --text-dim:    #4a5070;
  --text-faint:  #272d42;

  /* Category accent colours */
  --math:        #7eb8f7;   /* cool blue     */
  --physics:     #a78cf0;   /* violet        */
  --chemistry:   #6ddbb4;   /* teal-green    */
  --literature:  #f0a96e;   /* warm amber    */
  --notes:       #e07898;   /* rose          */

  /* Highlight */
  --gold:        #c8a96e;

  /* Typography */
  --font-serif:  'Crimson Pro', 'GFS Didot', Georgia, serif;
  --font-greek:  'GFS Didot', 'Crimson Pro', serif;
  --font-mono:   'JetBrains Mono', 'Courier New', monospace;

  /* Spacing */
  --max-width:   1100px;
  --gap:         20px;

  /* Misc */
  --radius:      4px;
  --transition:  0.22s ease;
}

/* ── SCROLLBAR ────────────────────────────────────────────── */
::-webkit-scrollbar               { width: 6px; height: 6px; }
::-webkit-scrollbar-track         { background: var(--bg); }
::-webkit-scrollbar-thumb         { background: var(--border-2); border-radius: 3px; }
::-webkit-scrollbar-thumb:hover   { background: var(--border-3); }

/* ── BASE ─────────────────────────────────────────────────── */
html { scroll-behavior: smooth; }

body {
  background: var(--bg);
  color: var(--text);
  font-family: var(--font-serif);
  font-size: 17px;
  line-height: 1.7;
  min-height: 100vh;
  -webkit-font-smoothing: antialiased;
}

/* Background canvas (animated dot field via JS) */
#bg-canvas {
  position: fixed;
  inset: 0;
  width: 100%;
  height: 100%;
  pointer-events: none;
  z-index: 0;
  opacity: 0.45;
}

/* Top accent bar */
body::after {
  content: '';
  position: fixed;
  top: 0; left: 0; right: 0;
  height: 2px;
  background: linear-gradient(
    90deg,
    transparent 0%,
    var(--math) 25%,
    var(--physics) 50%,
    var(--chemistry) 75%,
    transparent 100%
  );
  z-index: 200;
}

/* ── HEADER ───────────────────────────────────────────────── */
.site-header {
  position: relative;
  z-index: 10;
  border-bottom: 1px solid var(--border);
}

.header-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 56px 40px 36px;
  display: grid;
  grid-template-columns: 1fr auto;
  align-items: center;
  gap: 40px;
}

.site-eyebrow {
  font-family: var(--font-mono);
  font-size: 0.6rem;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--text-dim);
  margin-bottom: 14px;
}

.site-title {
  font-family: var(--font-greek);
  font-weight: normal;
  font-size: clamp(2.4rem, 5vw, 4rem);
  line-height: 1;
  letter-spacing: -0.02em;
  display: flex;
  align-items: baseline;
  gap: 16px;
  margin-bottom: 12px;
}

.title-greek {
  color: var(--text);
}

.title-amp {
  color: var(--text-dim);
  font-style: italic;
  font-size: 0.7em;
}

.title-math {
  color: var(--math);
  font-size: 0.75em;
}

.site-sub {
  font-family: var(--font-serif);
  font-style: italic;
  font-size: 0.95rem;
  color: var(--text-mid);
  letter-spacing: 0.01em;
}

.header-right {
  text-align: right;
}

.header-formula {
  font-size: 1.3rem;
  color: var(--gold);
  opacity: 0.8;
  padding: 16px 20px;
  border: 1px solid var(--border-2);
  background: var(--surface);
  border-radius: var(--radius);
  min-width: 160px;
}

/* ── TAB BAR ──────────────────────────────────────────────── */
.tab-bar {
  position: relative;
  z-index: 10;
  border-bottom: 1px solid var(--border);
  background: var(--bg);
}

.tab-bar-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 40px;
  display: flex;
  gap: 2px;
  overflow-x: auto;
  scrollbar-width: none;
}

.tab-bar-inner::-webkit-scrollbar { display: none; }

.tab {
  background: none;
  border: none;
  border-bottom: 2px solid transparent;
  margin-bottom: -1px;
  padding: 14px 16px 12px;
  font-family: var(--font-mono);
  font-size: 0.62rem;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--text-dim);
  cursor: pointer;
  white-space: nowrap;
  display: flex;
  align-items: center;
  gap: 8px;
  transition: color var(--transition), border-color var(--transition);
}

.tab:hover { color: var(--text-mid); }

.tab.active {
  color: var(--text);
  border-bottom-color: var(--text-mid);
}

/* Category-specific active colours */
.tab[data-cat="math"].active       { color: var(--math);       border-bottom-color: var(--math); }
.tab[data-cat="physics"].active    { color: var(--physics);    border-bottom-color: var(--physics); }
.tab[data-cat="chemistry"].active  { color: var(--chemistry);  border-bottom-color: var(--chemistry); }
.tab[data-cat="literature"].active { color: var(--literature); border-bottom-color: var(--literature); }
.tab[data-cat="notes"].active      { color: var(--notes);      border-bottom-color: var(--notes); }

.tab-dot {
  width: 6px; height: 6px;
  border-radius: 50%;
  background: currentColor;
  opacity: 0.5;
  flex-shrink: 0;
}

.tab.active .tab-dot { opacity: 1; }

.tab-count {
  font-size: 0.55rem;
  background: var(--surface-2);
  border: 1px solid var(--border-2);
  color: var(--text-dim);
  padding: 1px 7px;
  border-radius: 20px;
  min-width: 24px;
  text-align: center;
}

/* ── MAIN CONTENT ─────────────────────────────────────────── */
.main-content {
  position: relative;
  z-index: 1;
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 36px 40px 72px;
}

/* ── LOADING ──────────────────────────────────────────────── */
.loading-state {
  padding: 80px 20px;
  text-align: center;
}

.loading-text {
  font-family: var(--font-mono);
  font-size: 0.65rem;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--text-dim);
  animation: pulse 1.6s ease-in-out infinite;
}

@keyframes pulse {
  0%, 100% { opacity: 0.3; }
  50%       { opacity: 1; }
}

/* ── CARD GRID ────────────────────────────────────────────── */
.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(310px, 1fr));
  gap: var(--gap);
}

/* ── CARD ─────────────────────────────────────────────────── */
.card {
  --accent: var(--text-mid);   /* overridden per category */

  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 22px 24px 18px;
  text-decoration: none;
  color: inherit;
  display: flex;
  flex-direction: column;
  gap: 8px;
  position: relative;
  overflow: hidden;
  transition:
    border-color var(--transition),
    transform var(--transition),
    box-shadow var(--transition);

  /* stagger animation */
  animation: cardIn 0.4s ease backwards;
}

@keyframes cardIn {
  from { opacity: 0; transform: translateY(10px); }
  to   { opacity: 1; transform: translateY(0); }
}

/* Top colour stripe */
.card::before {
  content: '';
  position: absolute;
  top: 0; left: 0; right: 0;
  height: 2px;
  background: var(--accent);
  opacity: 0.5;
  transition: opacity var(--transition);
}

.card:hover {
  border-color: var(--border-2);
  transform: translateY(-3px);
  box-shadow: 0 12px 40px rgba(0,0,0,0.45);
}

.card:hover::before { opacity: 1; }

/* Per-category accent override */
.card[data-cat="math"]       { --accent: var(--math); }
.card[data-cat="physics"]    { --accent: var(--physics); }
.card[data-cat="chemistry"]  { --accent: var(--chemistry); }
.card[data-cat="literature"] { --accent: var(--literature); }
.card[data-cat="notes"]      { --accent: var(--notes); }

/* Card parts */
.card-tag {
  font-family: var(--font-mono);
  font-size: 0.58rem;
  text-transform: uppercase;
  letter-spacing: 0.14em;
  color: var(--accent);
}

.card-title {
  font-family: var(--font-greek);
  font-weight: normal;
  font-size: 1.15rem;
  line-height: 1.3;
  color: var(--text);
}

.card-formula {
  font-family: var(--font-serif);
  font-style: italic;
  font-size: 0.9rem;
  color: var(--gold);
  background: rgba(200,169,110,0.05);
  border-left: 2px solid rgba(200,169,110,0.25);
  padding: 8px 12px;
  margin: 4px 0;
  overflow-x: auto;
  border-radius: 0 var(--radius) var(--radius) 0;
}

.card-desc {
  font-family: var(--font-serif);
  font-size: 0.88rem;
  color: var(--text-mid);
  line-height: 1.65;
  flex: 1;
}

.card-footer {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding-top: 12px;
  border-top: 1px solid var(--border);
  margin-top: 4px;
}

.card-date {
  font-family: var(--font-mono);
  font-size: 0.57rem;
  letter-spacing: 0.06em;
  color: var(--text-dim);
}

.card-arrow {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--accent);
  opacity: 0.5;
  transition: opacity var(--transition), transform var(--transition);
}

.card:hover .card-arrow {
  opacity: 1;
  transform: translateX(4px);
}

/* Hidden cards (filtered out) */
.card.hidden { display: none; }

/* ── EMPTY STATE ──────────────────────────────────────────── */
.empty-state {
  grid-column: 1 / -1;
  padding: 80px 20px;
  text-align: center;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 14px;
}

.empty-math {
  font-family: var(--font-serif);
  font-style: italic;
  font-size: 2.5rem;
  color: var(--border-2);
}

.empty-label {
  font-family: var(--font-mono);
  font-size: 0.62rem;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--text-dim);
}

/* ── FOOTER ───────────────────────────────────────────────── */
.site-footer {
  position: relative;
  z-index: 1;
  border-top: 1px solid var(--border);
  background: var(--surface);
}

.footer-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 36px 40px 48px;
}

.footer-title {
  font-family: var(--font-mono);
  font-size: 0.6rem;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--text-dim);
  margin-bottom: 28px;
}

.footer-steps {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 28px;
}

.footer-step {
  display: flex;
  gap: 16px;
  align-items: flex-start;
}

.step-num {
  font-family: var(--font-serif);
  font-style: italic;
  font-size: 2rem;
  line-height: 1;
  color: var(--border-2);
  flex-shrink: 0;
  width: 36px;
}

.footer-step div {
  font-family: var(--font-mono);
  font-size: 0.62rem;
  line-height: 1.85;
  color: var(--text-dim);
}

.footer-step strong {
  display: block;
  color: var(--text-mid);
  font-size: 0.65rem;
  margin-bottom: 3px;
}

.footer-step code {
  background: var(--surface-3);
  border: 1px solid var(--border-2);
  color: var(--math);
  padding: 1px 6px;
  border-radius: 2px;
  font-size: 0.58rem;
}

/* ── UTILITIES ────────────────────────────────────────────── */
[hidden] { display: none !important; }

/* ── RESPONSIVE ───────────────────────────────────────────── */
@media (max-width: 700px) {
  .header-inner {
    grid-template-columns: 1fr;
    padding: 36px 20px 24px;
  }
  .header-right  { display: none; }
  .tab-bar-inner { padding: 0 20px; }
  .main-content  { padding: 24px 20px 48px; }
  .footer-inner  { padding: 28px 20px 40px; }
  .site-title    { font-size: 2.2rem; }
}

/* ── SUB-TAB BAR ──────────────────────────────────────────── */
.subtab-bar {
  position: relative;
  z-index: 9;
  border-bottom: 1px solid var(--border);
  background: var(--surface);
  --subcat-accent: var(--text-mid);
}

.subtab-bar-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 40px;
  display: flex;
  gap: 2px;
  overflow-x: auto;
  scrollbar-width: none;
}
.subtab-bar-inner::-webkit-scrollbar { display: none; }

.subtab {
  background: none;
  border: none;
  border-bottom: 2px solid transparent;
  margin-bottom: -1px;
  padding: 10px 14px 8px;
  font-family: var(--font-mono);
  font-size: 0.58rem;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--text-dim);
  cursor: pointer;
  white-space: nowrap;
  display: flex;
  align-items: center;
  gap: 8px;
  transition: color var(--transition), border-color var(--transition);
}

.subtab:hover { color: var(--text-mid); }

.subtab.active {
  color: var(--subcat-accent);
  border-bottom-color: var(--subcat-accent);
}

.subtab-count {
  font-size: 0.52rem;
  background: var(--surface-3);
  border: 1px solid var(--border-2);
  color: var(--text-dim);
  padding: 1px 6px;
  border-radius: 20px;
  min-width: 20px;
  text-align: center;
}

/* Sub-label on card tag */
.card-tag-sub {
  color: var(--text-dim);
  font-size: 0.9em;
}

@media (max-width: 700px) {
  .subtab-bar-inner { padding: 0 20px; }
}