:root {
  --bg: #f2f7fb;
  --panel: #ffffff;
  --ink: #16243a;
  --ink-soft: #5a6b84;
  --accent: #2f6fed;
  --accent-deep: #1d4fc4;
  --ice: #5ec8e5;
  --ice-soft: #e3f2fa;
  --danger: #c93b3b;
  --ok: #1f9d61;
  --radius: 14px;
  --shadow: 0 10px 30px rgba(22, 36, 58, 0.08);
  --font-display: "Sora", sans-serif;
  --font-body: "Public Sans", sans-serif;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  background:
    radial-gradient(1200px 500px at 80% -10%, var(--ice-soft), transparent),
    var(--bg);
  color: var(--ink);
  font-family: var(--font-body);
  line-height: 1.55;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

.wrap { width: min(920px, 92vw); margin: 0 auto; }

main.wrap { flex: 1; padding-bottom: 4rem; }

/* ---------- header ---------- */
.site-header {
  padding: 1.1rem 0;
  border-bottom: 1px solid rgba(22, 36, 58, 0.07);
  background: rgba(255, 255, 255, 0.65);
  backdrop-filter: blur(8px);
  position: sticky;
  top: 0;
  z-index: 10;
}
.header-inner { display: flex; align-items: center; justify-content: space-between; }
.logo {
  font-family: var(--font-display);
  font-weight: 800;
  font-size: 1.25rem;
  text-decoration: none;
  color: var(--ink);
}
.logo em { color: var(--accent); font-style: normal; }

/* ---------- hero ---------- */
.hero { text-align: center; margin: 3rem 0 2rem; }
.hero h1 {
  font-family: var(--font-display);
  font-size: clamp(1.8rem, 4.5vw, 2.9rem);
  font-weight: 800;
  letter-spacing: -0.02em;
  margin: 0 0 0.6rem;
}
.hero .accent {
  color: var(--accent);
  background: linear-gradient(120deg, var(--accent), var(--ice));
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
}
.hero p { color: var(--ink-soft); font-size: 1.1rem; margin: 0; }

/* ---------- panel / inputs ---------- */
.panel {
  background: var(--panel);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 1.6rem;
  margin-top: 1.5rem;
}

.dropzone {
  border: 2px dashed rgba(47, 111, 237, 0.35);
  border-radius: var(--radius);
  padding: 1.4rem;
  text-align: center;
  color: var(--ink-soft);
  background: var(--ice-soft);
  cursor: pointer;
  transition: border-color 0.15s, background 0.15s;
}
.dropzone.dragover { border-color: var(--accent); background: #d8ecf7; }
.dropzone .hint { display: block; margin-top: 0.3rem; font-size: 0.85rem; }
.dropzone-file { font-weight: 600; color: var(--ink); }

.link-btn {
  background: none;
  border: none;
  color: var(--accent);
  font: inherit;
  font-weight: 600;
  cursor: pointer;
  padding: 0;
  text-decoration: underline;
}

.or-divider {
  display: flex;
  align-items: center;
  gap: 0.8rem;
  color: var(--ink-soft);
  font-size: 0.85rem;
  margin: 1.2rem 0 0.8rem;
}
.or-divider::before, .or-divider::after {
  content: "";
  flex: 1;
  height: 1px;
  background: rgba(22, 36, 58, 0.1);
}

textarea {
  width: 100%;
  border: 1px solid rgba(22, 36, 58, 0.15);
  border-radius: 10px;
  padding: 0.9rem;
  font: inherit;
  resize: vertical;
  color: var(--ink);
}
textarea:focus { outline: 2px solid var(--accent); outline-offset: 1px; border-color: transparent; }

.char-count { text-align: right; color: var(--ink-soft); font-size: 0.8rem; min-height: 1.2em; margin-top: 0.25rem; }

.options {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 1rem;
  margin: 1.2rem 0 1.4rem;
}
.options label {
  display: flex;
  flex-direction: column;
  gap: 0.4rem;
  font-weight: 600;
  font-size: 0.92rem;
}
.options output { color: var(--accent); }
.options select {
  font: inherit;
  padding: 0.5rem;
  border-radius: 8px;
  border: 1px solid rgba(22, 36, 58, 0.15);
  background: #fff;
}
input[type="range"] { accent-color: var(--accent); }

.primary-btn {
  display: block;
  width: 100%;
  background: linear-gradient(120deg, var(--accent), var(--accent-deep));
  color: #fff;
  border: none;
  border-radius: 12px;
  padding: 0.95rem 1.4rem;
  font-family: var(--font-display);
  font-size: 1.05rem;
  font-weight: 700;
  cursor: pointer;
  transition: transform 0.1s, box-shadow 0.15s;
  box-shadow: 0 6px 18px rgba(47, 111, 237, 0.35);
}
.primary-btn:hover { transform: translateY(-1px); }
.primary-btn:disabled { opacity: 0.6; cursor: wait; transform: none; }

.turnstile-box { display: flex; justify-content: center; margin-bottom: 1rem; }

.ghost-btn {
  background: #fff;
  border: 1px solid rgba(22, 36, 58, 0.18);
  border-radius: 10px;
  padding: 0.5rem 0.9rem;
  font: inherit;
  font-weight: 600;
  color: var(--ink);
  cursor: pointer;
}
.ghost-btn:hover { border-color: var(--accent); color: var(--accent); }

.error { color: var(--danger); font-weight: 600; margin-top: 0.8rem; }

.demo-banner {
  background: #fff6e0;
  border: 1px solid #eccd77;
  border-radius: 10px;
  padding: 0.7rem 1rem;
  margin-top: 1.2rem;
  font-size: 0.92rem;
}

/* ---------- loading ---------- */
.loading { text-align: center; padding: 6rem 0; color: var(--ink-soft); }
.blitz-spinner {
  font-size: 3rem;
  display: inline-block;
  animation: blitz-pulse 1.1s ease-in-out infinite;
}
@keyframes blitz-pulse {
  0%, 100% { transform: scale(1); opacity: 0.5; }
  50% { transform: scale(1.28); opacity: 1; filter: drop-shadow(0 0 14px rgba(47, 111, 237, 0.55)); }
}

/* ---------- results ---------- */
.results-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  margin: 2rem 0 1rem;
  flex-wrap: wrap;
}
.results-header h2 {
  font-family: var(--font-display);
  font-size: 1.5rem;
  margin: 0;
}

.tabs { display: flex; gap: 0.5rem; margin-bottom: 1.2rem; }
.tab {
  background: #fff;
  border: 1px solid rgba(22, 36, 58, 0.15);
  border-radius: 999px;
  padding: 0.5rem 1.1rem;
  font: inherit;
  font-weight: 600;
  cursor: pointer;
  color: var(--ink-soft);
}
.tab.active { background: var(--ink); border-color: var(--ink); color: #fff; }

/* flashcards */
.flashcard-stage { text-align: center; }
.flashcard {
  perspective: 1200px;
  max-width: 560px;
  height: 320px;
  margin: 0 auto;
  cursor: pointer;
  outline: none;
}
.flashcard-inner {
  position: relative;
  width: 100%;
  height: 100%;
  transform-style: preserve-3d;
  transition: transform 0.45s cubic-bezier(0.4, 0.1, 0.2, 1);
}
.flashcard.flipped .flashcard-inner { transform: rotateY(180deg); }
.flashcard-face {
  position: absolute;
  inset: 0;
  backface-visibility: hidden;
  background: var(--panel);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 1.6rem;
  overflow-y: auto;
}
.flashcard-back { transform: rotateY(180deg); background: linear-gradient(150deg, #f0f7ff, #fff); }
.face-label {
  position: absolute;
  top: 0.9rem;
  left: 1.1rem;
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--ice);
}
.flashcard-back .face-label { color: var(--accent); }
.flashcard-face p {
  font-family: var(--font-display);
  font-size: 1.25rem;
  font-weight: 600;
  margin: 0;
}
.flip-hint { color: var(--ink-soft); font-size: 0.82rem; margin: 0.8rem 0 1rem; }
.deck-controls {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0.7rem;
  flex-wrap: wrap;
}
.card-counter { font-weight: 700; font-family: var(--font-display); min-width: 4.5rem; }

/* quiz */
.quiz-q {
  background: var(--panel);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 1.2rem 1.4rem;
  margin-bottom: 1rem;
}
.quiz-q h3 { margin: 0 0 0.8rem; font-size: 1.02rem; }
.quiz-q h3 .qnum { color: var(--accent); margin-right: 0.4rem; }
.quiz-opt {
  display: flex;
  gap: 0.6rem;
  align-items: baseline;
  padding: 0.55rem 0.7rem;
  border-radius: 8px;
  cursor: pointer;
  border: 1px solid transparent;
}
.quiz-opt:hover { background: var(--ice-soft); }
.quiz-opt input { accent-color: var(--accent); }
.quiz-q.graded .quiz-opt { cursor: default; }
.quiz-q.graded .quiz-opt:hover { background: none; }
.quiz-opt.correct { background: #e7f6ee; border-color: var(--ok); }
.quiz-opt.wrong { background: #fdeaea; border-color: var(--danger); }
.quiz-explain {
  margin: 0.7rem 0 0;
  padding: 0.7rem 0.9rem;
  background: var(--ice-soft);
  border-radius: 8px;
  font-size: 0.92rem;
  color: var(--ink-soft);
}
.quiz-footer { text-align: center; margin-top: 1.4rem; }
.quiz-footer .primary-btn { max-width: 320px; margin: 0 auto; }
.quiz-score {
  font-family: var(--font-display);
  font-size: 1.4rem;
  font-weight: 800;
  margin: 1rem 0;
}
#retryQuizBtn { margin-top: 0.3rem; }

/* saved sets */
.saved-list { list-style: none; padding: 0; margin: 1rem 0; display: grid; gap: 0.7rem; }
.saved-list li {
  background: var(--panel);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 0.9rem 1.2rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
}
.saved-list .set-name { font-weight: 700; font-family: var(--font-display); cursor: pointer; }
.saved-list .set-name:hover { color: var(--accent); }
.saved-list .set-meta { color: var(--ink-soft); font-size: 0.85rem; }
.saved-list .del-btn { color: var(--danger); }

.hint { color: var(--ink-soft); font-size: 0.9rem; }

/* footer */
.site-footer {
  border-top: 1px solid rgba(22, 36, 58, 0.07);
  padding: 1.2rem 0;
  color: var(--ink-soft);
  font-size: 0.85rem;
  text-align: center;
}

@media (max-width: 560px) {
  .flashcard { height: 260px; }
  .panel { padding: 1.1rem; }
}