:root {
  --bg: #0f172a;
  --panel: #111827;
  --panel-light: #1f2937;
  --text: #f8fafc;
  --muted: #cbd5e1;
  --accent: #38bdf8;
  --accent-dark: #0284c7;
  --success: #22c55e;
  --danger: #ef4444;
  --border: rgba(148, 163, 184, 0.25);
  --shadow: 0 24px 70px rgba(0, 0, 0, 0.35);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  background:
    radial-gradient(circle at top left, rgba(56, 189, 248, 0.18), transparent 28rem),
    linear-gradient(135deg, #020617, var(--bg));
  color: var(--text);
  font-family: Inter, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
}

button,
input,
select {
  font: inherit;
}

button {
  border: 0;
  border-radius: 999px;
  padding: 0.85rem 1.1rem;
  background: var(--accent);
  color: #082f49;
  font-weight: 800;
  cursor: pointer;
  transition: transform 0.2s ease, background-color 0.2s ease;
}

button:hover {
  background: #7dd3fc;
  transform: translateY(-1px);
}

button.secondary {
  background: rgba(148, 163, 184, 0.16);
  color: var(--text);
}

input,
select {
  width: 100%;
  border: 1px solid var(--border);
  border-radius: 0.9rem;
  padding: 0.85rem 1rem;
  background: rgba(15, 23, 42, 0.82);
  color: var(--text);
  outline: none;
}

input::placeholder {
  color: #94a3b8;
}

input:focus,
select:focus {
  border-color: var(--accent);
  box-shadow: 0 0 0 3px rgba(56, 189, 248, 0.2);
}

.app-shell {
  width: min(1080px, calc(100% - 2rem));
  margin: 0 auto;
  padding: 2rem 0 3rem;
}

.hero {
  text-align: center;
  margin-bottom: 1.5rem;
}

.eyebrow {
  margin: 0 0 0.4rem;
  color: var(--accent);
  font-weight: 800;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.hero h1 {
  margin: 0;
  font-size: clamp(2.5rem, 7vw, 4.8rem);
  line-height: 0.95;
}

.hero p:last-child {
  max-width: 680px;
  margin: 1rem auto 0;
  color: var(--muted);
  font-size: 1.05rem;
}

.controls,
.stats,
.study-area,
.add-card-panel,
.card-list-panel {
  border: 1px solid var(--border);
  border-radius: 1.5rem;
  background: rgba(15, 23, 42, 0.72);
  box-shadow: var(--shadow);
  backdrop-filter: blur(18px);
}

.controls {
  display: grid;
  grid-template-columns: auto minmax(180px, 1fr) auto auto;
  align-items: center;
  gap: 0.8rem;
  padding: 1rem;
  margin-bottom: 1rem;
}

.controls label {
  color: var(--muted);
  font-weight: 800;
}

.stats {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 1rem;
  padding: 1rem;
  margin-bottom: 1rem;
}

.stats article {
  border-radius: 1rem;
  background: rgba(30, 41, 59, 0.72);
  padding: 1rem;
  text-align: center;
}

.stats span {
  display: block;
  color: var(--muted);
  font-size: 0.82rem;
  font-weight: 800;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.stats strong {
  display: block;
  margin-top: 0.3rem;
  font-size: 1.8rem;
}

.study-area {
  padding: 1.2rem;
  text-align: center;
  margin-bottom: 1rem;
}

.flashcard {
  width: min(100%, 520px);
  min-height: 280px;
  margin: 0 auto;
  border: 1px solid rgba(56, 189, 248, 0.35);
  border-radius: 1.4rem;
  background: linear-gradient(145deg, #0ea5e9, #2563eb);
  color: white;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  cursor: pointer;
  padding: 2rem;
  transition: transform 0.25s ease, box-shadow 0.25s ease, background-color 0.25s ease;
  box-shadow: 0 18px 55px rgba(37, 99, 235, 0.35);
}

.flashcard:hover,
.flashcard:focus-visible {
  transform: translateY(-4px) scale(1.01);
  box-shadow: 0 22px 65px rgba(56, 189, 248, 0.42);
}

.flashcard.showing-definition {
  background: linear-gradient(145deg, #16a34a, #059669);
  box-shadow: 0 18px 55px rgba(22, 163, 74, 0.32);
}

#card-label {
  margin: 0 0 1rem;
  color: rgba(255, 255, 255, 0.75);
  font-weight: 800;
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

#card-content {
  margin: 0;
  font-size: clamp(1.8rem, 6vw, 3.1rem);
  font-weight: 900;
}

.flashcard small {
  margin-top: 1.4rem;
  color: rgba(255, 255, 255, 0.78);
}

.card-meta {
  display: flex;
  justify-content: center;
  gap: 1rem;
  flex-wrap: wrap;
  margin: 1rem 0;
  color: var(--muted);
  font-weight: 700;
}

.buttons,
.form-grid {
  display: flex;
  justify-content: center;
  gap: 0.8rem;
  flex-wrap: wrap;
}

.add-card-panel,
.card-list-panel {
  padding: 1.2rem;
  margin-bottom: 1rem;
}

.add-card-panel h2,
.card-list-panel h2 {
  margin: 0 0 1rem;
}

.form-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
}

#status-message {
  min-height: 1.4rem;
  color: var(--success);
  font-weight: 700;
}

.card-list {
  display: grid;
  gap: 0.75rem;
}

.card-list-item {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  align-items: center;
  border: 1px solid var(--border);
  border-radius: 1rem;
  padding: 1rem;
  background: rgba(30, 41, 59, 0.66);
  text-align: left;
}

.card-list-item p {
  margin: 0.2rem 0;
  color: var(--muted);
}

.card-list-item small {
  color: var(--accent);
  font-weight: 800;
}

.card-list-item button {
  background: rgba(239, 68, 68, 0.16);
  color: #fecaca;
}

@media (max-width: 760px) {
  .controls,
  .stats,
  .form-grid {
    grid-template-columns: 1fr;
  }

  .card-list-item {
    align-items: stretch;
    flex-direction: column;
  }
}