:root {
  color-scheme: dark;
  --bg: #0f1220;
  --panel: #171b2f;
  --panel-border: #2a3150;
  --text: #edf1ff;
  --muted: #aab4d6;
  --primary: #6f8dff;
  --primary-hover: #87a0ff;
  --secondary: #242b47;
  --secondary-hover: #303a60;
  --good: #7dd3a6;
  --danger: #dc6f7f;
  --danger-hover: #e18290;
  --success: #4ca176;
  --success-hover: #5db385;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: Inter, system-ui, -apple-system, Segoe UI, Roboto, Helvetica, Arial, sans-serif;
  background: radial-gradient(circle at top, #1b2040, var(--bg) 56%);
  color: var(--text);
  min-height: 100vh;
  padding: 24px;
}

.app {
  max-width: 980px;
  margin: 0 auto;
  display: grid;
  gap: 16px;
}

.app-header h1 {
  margin: 0;
  font-size: clamp(1.6rem, 2vw, 2rem);
}

.app-header p {
  margin: 8px 0 0;
  color: var(--muted);
}

.panel {
  background: color-mix(in srgb, var(--panel) 92%, white 8%);
  border: 1px solid var(--panel-border);
  border-radius: 14px;
  padding: 14px;
}

.controls {
  display: grid;
  gap: 8px;
}

.control-group,
.toolbar-row {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

.info-row {
  color: var(--muted);
  justify-content: space-between;
  font-size: 0.95rem;
}

.toggle-wrap {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 8px 10px;
  background: #252f53;
  border: 1px solid #3d4a75;
  border-radius: 10px;
  color: var(--muted);
  font-size: 0.92rem;
}

.toggle-wrap input {
  width: 16px;
  height: 16px;
}

.progress-block {
  display: grid;
  gap: 6px;
}

.progress-head {
  display: flex;
  justify-content: space-between;
  align-items: center;
  color: var(--muted);
  font-size: 0.95rem;
}

.progress-track {
  width: 100%;
  height: 10px;
  background: #202744;
  border: 1px solid #394267;
  border-radius: 999px;
  overflow: hidden;
}

.progress-bar {
  width: 0%;
  height: 100%;
  background: linear-gradient(90deg, #5f7fff, #79a2ff);
  transition: width 0.25s ease;
}

.attempts-text {
  color: var(--muted);
  font-size: 0.9rem;
}

.btn {
  border: 1px solid transparent;
  border-radius: 10px;
  padding: 10px 14px;
  font-size: 0.95rem;
  color: var(--text);
  cursor: pointer;
  transition: background 0.15s ease, transform 0.1s ease;
}

.btn:active {
  transform: translateY(1px);
}

.btn-primary {
  background: var(--primary);
}

.btn-primary:hover {
  background: var(--primary-hover);
}

.btn-secondary {
  background: var(--secondary);
  border-color: #394267;
}

.btn-secondary:hover {
  background: var(--secondary-hover);
}

.btn-success {
  background: var(--success);
}

.btn-success:hover {
  background: var(--success-hover);
}

.btn-danger {
  background: var(--danger);
}

.btn-danger:hover {
  background: var(--danger-hover);
}

.btn:disabled {
  opacity: 0.45;
  cursor: not-allowed;
}

#fileInput {
  position: absolute;
  width: 1px;
  height: 1px;
  opacity: 0;
  pointer-events: none;
}

.status {
  margin: 0;
  color: var(--muted);
}

.card-panel {
  perspective: 1200px;
}

.flashcard {
  min-height: 320px;
  border-radius: 16px;
  border: 1px solid #404b74;
  background: linear-gradient(140deg, #1c2140, #171b33);
  box-shadow: 0 20px 45px rgba(0, 0, 0, 0.26);
  position: relative;
  transform-style: preserve-3d;
  transition: transform 0.55s ease;
  cursor: pointer;
  padding: 18px;
}

.flashcard.is-flipped {
  transform: rotateY(180deg);
}

.card-face {
  position: absolute;
  inset: 0;
  padding: 18px;
  backface-visibility: hidden;
  display: grid;
  grid-template-rows: auto 1fr;
  gap: 8px;
}

.card-back {
  transform: rotateY(180deg);
}

.card-face h2 {
  margin: 0;
  font-size: 1rem;
  letter-spacing: 0.04em;
  color: var(--muted);
  text-transform: uppercase;
}

.card-content {
  overflow: auto;
  white-space: normal;
  line-height: 1.55;
  font-size: 1.03rem;
  padding-right: 4px;
}

.card-content strong {
  color: #f9fbff;
}

.card-content em {
  color: #d6ddfa;
}

.card-content ul,
.card-content ol {
  margin: 0.25rem 0 0.5rem 1.1rem;
  padding: 0;
}

.card-content code {
  background: #2c3659;
  border: 1px solid #3e4b77;
  border-radius: 6px;
  padding: 0.1rem 0.3rem;
  font-size: 0.9rem;
}

.is-empty {
  color: var(--good);
}

.katex-display {
  margin: 0.55rem 0;
  overflow-x: auto;
  overflow-y: hidden;
}

.help p {
  margin: 0;
  color: var(--muted);
  font-size: 0.95rem;
}

@media (max-width: 720px) {
  body {
    padding: 14px;
  }

  .flashcard {
    min-height: 390px;
  }

  .btn {
    width: 100%;
  }

  .control-group label.btn {
    text-align: center;
  }
}