:root {
  --bg: #0d1117;
  --bg-elev: #161b22;
  --bg-elev2: #1c2330;
  --line: #2a3240;
  --line-soft: #222a36;
  --text: #e6edf3;
  --text-dim: #9aa7b4;
  --text-faint: #6b7888;
  --accent: #6ea8fe;
  --accent-dim: #2d4a73;
  --known: #3fb950;
  --review: #d29922;
  --radius: 14px;
  --maxw: 1180px;
  --font: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--font);
  line-height: 1.55;
  -webkit-font-smoothing: antialiased;
}

/* ---------- Top bar ---------- */
.topbar {
  position: sticky;
  top: 0;
  z-index: 20;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  flex-wrap: wrap;
  padding: 0.9rem clamp(1rem, 4vw, 2.5rem);
  background: rgba(13, 17, 23, 0.85);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--line);
}
.brand h1 { margin: 0; font-size: 1.15rem; letter-spacing: -0.01em; }
.tagline { margin: 0.1rem 0 0; font-size: 0.8rem; color: var(--text-dim); }

.viewtoggle {
  display: inline-flex;
  background: var(--bg-elev);
  border: 1px solid var(--line);
  border-radius: 999px;
  padding: 3px;
}
.viewtoggle__btn {
  appearance: none;
  border: 0;
  background: transparent;
  color: var(--text-dim);
  font: inherit;
  font-size: 0.85rem;
  font-weight: 600;
  padding: 0.4rem 1.05rem;
  border-radius: 999px;
  cursor: pointer;
  transition: color 0.15s, background 0.15s;
}
.viewtoggle__btn.is-active {
  background: var(--accent);
  color: #0a0f16;
}

/* ---------- Views ---------- */
.view { display: none; }
.view.is-active { display: block; }

main { max-width: var(--maxw); margin: 0 auto; padding: 1.5rem clamp(1rem, 4vw, 2.5rem) 4rem; }

/* ---------- Overview ---------- */
#view-overview.is-active { display: grid; grid-template-columns: 200px 1fr; gap: 2rem; align-items: start; }

.sidenav {
  position: sticky;
  top: 92px;
  display: flex;
  flex-direction: column;
  gap: 2px;
  font-size: 0.85rem;
}
.sidenav a {
  color: var(--text-dim);
  text-decoration: none;
  padding: 0.35rem 0.6rem;
  border-radius: 8px;
  border-left: 2px solid transparent;
  transition: background 0.15s, color 0.15s;
}
.sidenav a:hover { background: var(--bg-elev); color: var(--text); }
.sidenav a.active { color: var(--accent); border-left-color: var(--accent); background: var(--bg-elev); }

.lede {
  font-size: 1.02rem;
  color: var(--text-dim);
  background: var(--bg-elev);
  border: 1px solid var(--line-soft);
  border-radius: var(--radius);
  padding: 1.1rem 1.3rem;
  margin: 0 0 2rem;
}
.lede strong { color: var(--text); }

.cat-section { margin-bottom: 2.6rem; scroll-margin-top: 92px; }
.cat-section__head {
  display: flex;
  align-items: baseline;
  gap: 0.6rem;
  margin: 0 0 1rem;
  padding-bottom: 0.5rem;
  border-bottom: 1px solid var(--line);
}
.cat-section__head h2 { margin: 0; font-size: 1.05rem; letter-spacing: 0.02em; text-transform: uppercase; color: var(--accent); }
.cat-section__count { font-size: 0.8rem; color: var(--text-faint); }

.term-card {
  background: var(--bg-elev);
  border: 1px solid var(--line-soft);
  border-radius: var(--radius);
  padding: 1.1rem 1.25rem;
  margin-bottom: 0.9rem;
}
.term-card__head { display: flex; align-items: baseline; gap: 0.6rem; flex-wrap: wrap; margin-bottom: 0.7rem; }
.term-card__term { font-size: 1.1rem; font-weight: 700; letter-spacing: -0.01em; }
.term-card__full { font-size: 0.85rem; color: var(--text-faint); font-style: italic; }

.term-card__blocks { display: grid; gap: 0.7rem; }
.block-label {
  display: inline-block;
  font-size: 0.68rem;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  font-weight: 700;
  color: var(--text-faint);
  margin-bottom: 0.1rem;
}
.block-label.is-here { color: var(--accent); }
.term-card__blocks p { margin: 0; font-size: 0.92rem; }
.term-card__blocks .here-text { color: var(--text); }
.term-card__blocks .gen-text { color: var(--text-dim); }
.block--here {
  background: var(--bg-elev2);
  border-left: 2px solid var(--accent);
  border-radius: 0 8px 8px 0;
  padding: 0.55rem 0.75rem;
}

/* ---------- Flashcards ---------- */
.cards-toolbar { max-width: 640px; margin: 0 auto 1.5rem; }
.cards-toolbar__row { display: flex; align-items: flex-end; justify-content: space-between; gap: 1rem; flex-wrap: wrap; }
.cards-toolbar__actions { display: flex; gap: 0.5rem; }
.field { display: flex; flex-direction: column; gap: 0.3rem; font-size: 0.75rem; color: var(--text-dim); text-transform: uppercase; letter-spacing: 0.05em; }
.field select {
  appearance: none;
  background: var(--bg-elev);
  color: var(--text);
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 0.45rem 2rem 0.45rem 0.7rem;
  font: inherit;
  font-size: 0.9rem;
  cursor: pointer;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='10' height='6' viewBox='0 0 10 6'%3E%3Cpath fill='%239aa7b4' d='M0 0l5 6 5-6z'/%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: right 0.7rem center;
}

.btn {
  appearance: none;
  border: 1px solid var(--line);
  background: var(--bg-elev);
  color: var(--text);
  font: inherit;
  font-size: 0.85rem;
  font-weight: 600;
  padding: 0.45rem 0.95rem;
  border-radius: 8px;
  cursor: pointer;
  transition: background 0.15s, border-color 0.15s, transform 0.05s;
}
.btn:hover { background: var(--bg-elev2); }
.btn:active { transform: translateY(1px); }
.btn--ghost { background: transparent; color: var(--text-dim); }
.btn--flip { background: var(--accent-dim); border-color: var(--accent-dim); color: var(--text); }
.btn--known { border-color: var(--known); color: var(--known); }
.btn--known:hover { background: rgba(63, 185, 80, 0.12); }
.btn--review { border-color: var(--review); color: var(--review); }
.btn--review:hover { background: rgba(210, 153, 34, 0.12); }

.progress { margin-top: 1rem; }
.progress__stats { display: flex; gap: 1.2rem; font-size: 0.8rem; color: var(--text-dim); margin-bottom: 0.4rem; }
.progress__stats strong { color: var(--text); }
.progress__bar { height: 6px; background: var(--bg-elev); border-radius: 999px; overflow: hidden; border: 1px solid var(--line-soft); }
.progress__fill { height: 100%; width: 0%; background: linear-gradient(90deg, var(--known), var(--accent)); transition: width 0.3s ease; }

.flashcard-stage { max-width: 640px; margin: 0 auto; }

.flashcard {
  perspective: 1600px;
  width: 100%;
  aspect-ratio: 3 / 2;
  cursor: pointer;
  outline: none;
}
.flashcard:focus-visible .flashcard__inner { box-shadow: 0 0 0 2px var(--accent); border-radius: var(--radius); }
.flashcard__inner {
  position: relative;
  width: 100%;
  height: 100%;
  transition: transform 0.55s cubic-bezier(0.4, 0.0, 0.2, 1);
  transform-style: preserve-3d;
}
.flashcard.is-flipped .flashcard__inner { transform: rotateY(180deg); }

.flashcard__face {
  position: absolute;
  inset: 0;
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
  border-radius: var(--radius);
  border: 1px solid var(--line);
  background: var(--bg-elev);
  display: flex;
  flex-direction: column;
  padding: 1.5rem;
}
.flashcard__front { align-items: center; justify-content: center; text-align: center; gap: 0.5rem; }
.flashcard__term { font-size: clamp(1.8rem, 6vw, 2.6rem); font-weight: 800; letter-spacing: -0.02em; }
.flashcard__full { color: var(--text-dim); font-size: 0.95rem; font-style: italic; }
.flashcard__hint { position: absolute; bottom: 1rem; font-size: 0.72rem; color: var(--text-faint); letter-spacing: 0.04em; }

.flashcard__back { transform: rotateY(180deg); padding: 0; }
.flashcard__back-scroll { overflow-y: auto; padding: 1.3rem 1.4rem; display: grid; gap: 0.85rem; }
.back-block .back-label {
  display: block;
  font-size: 0.66rem;
  text-transform: uppercase;
  letter-spacing: 0.07em;
  font-weight: 700;
  color: var(--text-faint);
  margin-bottom: 0.2rem;
}
.back-block p { margin: 0; font-size: 0.9rem; color: var(--text-dim); }
.back-block--accent {
  background: var(--bg-elev2);
  border-left: 2px solid var(--accent);
  border-radius: 0 8px 8px 0;
  padding: 0.6rem 0.8rem;
}
.back-block--accent .back-label { color: var(--accent); }
.back-block--accent p { color: var(--text); }

.chip {
  font-size: 0.68rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  font-weight: 700;
  color: var(--accent);
  background: var(--accent-dim);
  padding: 0.18rem 0.6rem;
  border-radius: 999px;
}

.card-controls { display: flex; gap: 0.7rem; justify-content: center; margin-top: 1.3rem; }
.card-controls .btn { min-width: 116px; padding: 0.6rem 1rem; }

.deck-empty { text-align: center; padding: 2rem 1rem; color: var(--text-dim); }
.deck-empty p { margin: 0 0 1rem; }

/* ---------- Footer ---------- */
.footer {
  max-width: var(--maxw);
  margin: 0 auto;
  padding: 1.5rem clamp(1rem, 4vw, 2.5rem) 2.5rem;
  border-top: 1px solid var(--line-soft);
}
.footer p { margin: 0; font-size: 0.75rem; color: var(--text-faint); }

/* ---------- Responsive ---------- */
@media (max-width: 760px) {
  #view-overview.is-active { grid-template-columns: 1fr; }
  .sidenav { position: static; flex-direction: row; flex-wrap: wrap; margin-bottom: 1rem; }
  .sidenav a { border-left: 0; border-bottom: 2px solid transparent; }
  .sidenav a.active { border-left: 0; border-bottom-color: var(--accent); }
  .card-controls { flex-wrap: wrap; }
  .card-controls .btn { flex: 1 1 30%; min-width: 0; }
}