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

:root {
  --bg:           #F5F2EB;
  --surface:      #FFFFFF;
  --primary:      #3D5AF1;
  --primary-dim:  #EEF0FD;
  --know:         #27AE60;
  --know-dim:     #C8F0D8;
  --miss:         #E74C3C;
  --miss-dim:     #F9CECA;
  --text:         #1A1A2E;
  --muted:        #8892A4;
  --border:       #E5E0D8;
  --radius-lg:    20px;
  --radius-md:    12px;
  --radius-sm:    8px;
  --shadow:       0 4px 24px rgba(0, 0, 0, 0.08);
  --shadow-hover: 0 8px 32px rgba(0, 0, 0, 0.13);
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', system-ui, sans-serif;
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
}

/* ── Screens ────────────────────────────────────────────────────────────── */
.screen {
  display: none;
  width: 100%;
  min-height: 100vh;
  align-items: center;
  justify-content: center;
}

.screen.active {
  display: flex;
}

.container {
  width: 100%;
  max-width: 480px;
  padding: 2.5rem 1.5rem;
  display: flex;
  flex-direction: column;
  gap: 1.25rem;
}

/* ── URL Screen ─────────────────────────────────────────────────────────── */
.logo {
  font-size: 2.75rem;
  font-weight: 800;
  letter-spacing: -1.5px;
  color: var(--primary);
}

.tagline {
  color: var(--muted);
  font-size: 1rem;
  margin-top: -0.5rem;
}

.input-group {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.input-group label {
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text);
}

.input-group input {
  width: 100%;
  padding: 0.875rem 1rem;
  border: 2px solid var(--border);
  border-radius: var(--radius-md);
  font-size: 0.9375rem;
  color: var(--text);
  background: var(--surface);
  outline: none;
  transition: border-color 0.2s;
}

.input-group input:focus {
  border-color: var(--primary);
}

.error {
  color: var(--miss);
  font-size: 0.875rem;
  padding: 0.75rem 1rem;
  background: var(--miss-dim);
  border-radius: var(--radius-sm);
}

.hidden {
  display: none !important;
}

/* ── Buttons ────────────────────────────────────────────────────────────── */
.btn {
  padding: 0.9rem 1.5rem;
  border: none;
  border-radius: var(--radius-md);
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  transition: transform 0.15s, box-shadow 0.15s;
  text-align: center;
}

.btn:active {
  transform: scale(0.97);
}

.btn:disabled {
  opacity: 0.55;
  cursor: not-allowed;
}

.btn-primary {
  background: var(--primary);
  color: #fff;
  box-shadow: 0 4px 14px rgba(61, 90, 241, 0.35);
}

.btn-primary:hover:not(:disabled) {
  box-shadow: 0 6px 18px rgba(61, 90, 241, 0.45);
}

.btn-secondary {
  background: var(--surface);
  color: var(--text);
  border: 2px solid var(--border);
}

.btn-secondary:hover:not(:disabled) {
  border-color: var(--primary);
}

.btn-back {
  background: none;
  border: none;
  color: var(--primary);
  font-size: 0.9375rem;
  font-weight: 500;
  cursor: pointer;
  padding: 0;
  align-self: flex-start;
}

/* ── Deck Picker ────────────────────────────────────────────────────────── */
.deck-list {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
}

.deck-item {
  padding: 1.25rem 1.5rem;
  background: var(--surface);
  border: 2px solid var(--border);
  border-radius: var(--radius-lg);
  color: var(--text);
  cursor: pointer;
  text-align: left;
  box-shadow: var(--shadow);
  transition: border-color 0.2s, box-shadow 0.2s, transform 0.15s;
  display: flex;
  flex-direction: column;
  gap: 0.25rem;
}

.deck-item:hover {
  border-color: var(--primary);
  box-shadow: var(--shadow-hover);
  transform: translateY(-2px);
}

.deck-item:active {
  transform: translateY(0);
}

.deck-item-name {
  font-size: 1.0625rem;
  font-weight: 600;
}

.deck-item-desc {
  font-size: 0.875rem;
  color: var(--muted);
  font-weight: 400;
}

/* ── Ready Screen ───────────────────────────────────────────────────────── */
.ready-info {
  display: flex;
  flex-direction: column;
  gap: 0.375rem;
}

.ready-deck-desc {
  color: var(--muted);
  font-size: 0.9375rem;
}

.session-size-wrap {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
}

.session-size-label {
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text);
}

.settings-row {
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.toggle-row {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  cursor: pointer;
}

.toggle-label {
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text);
}

.toggle-row input[type="checkbox"] {
  width: 1.125rem;
  height: 1.125rem;
  accent-color: var(--primary);
  cursor: pointer;
}

.session-size-options {
  display: flex;
  gap: 0.5rem;
}

.size-btn {
  flex: 1;
  padding: 0.75rem 0.5rem;
  border: 2px solid var(--border);
  border-radius: var(--radius-md);
  background: var(--surface);
  font-size: 0.9375rem;
  font-weight: 600;
  color: var(--muted);
  cursor: pointer;
  transition: border-color 0.15s, background 0.15s, color 0.15s;
}

.size-btn.active {
  border-color: var(--primary);
  background: var(--primary-dim);
  color: var(--primary);
}

.size-slider-wrap {
  display: flex;
  align-items: center;
  gap: 1rem;
  width: 100%;
}

.size-slider {
  flex: 1;
  -webkit-appearance: none;
  appearance: none;
  height: 4px;
  border-radius: 2px;
  background: var(--border);
  outline: none;
  cursor: pointer;
  accent-color: var(--primary);
}

.size-slider::-webkit-slider-thumb {
  -webkit-appearance: none;
  appearance: none;
  width: 22px;
  height: 22px;
  border-radius: 50%;
  background: var(--primary);
  cursor: pointer;
  border: none;
  box-shadow: 0 1px 4px rgba(61, 90, 241, 0.3);
}

.size-slider::-moz-range-thumb {
  width: 22px;
  height: 22px;
  border-radius: 50%;
  background: var(--primary);
  cursor: pointer;
  border: none;
  box-shadow: 0 1px 4px rgba(61, 90, 241, 0.3);
}

.size-slider-value {
  font-size: 0.9375rem;
  font-weight: 700;
  color: var(--primary);
  min-width: 2.5rem;
  text-align: right;
}

/* ── Study Layout ───────────────────────────────────────────────────────── */
#screen-decks,
#screen-ready,
#screen-summary {
  align-items: flex-start;
}

.study-layout {
  width: 100%;
  max-width: 480px;
  min-height: 100vh;
  padding: 2.5rem 1.5rem 1.5rem;
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
}

.study-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.progress-text {
  font-size: 0.8125rem;
  font-weight: 600;
  color: var(--muted);
}

/* ── Progress Bar ───────────────────────────────────────────────────────── */
.progress-bar-wrap {
  height: 7px;
  background: var(--border);
  border-radius: 99px;
  overflow: hidden;
}

.progress-bar {
  height: 100%;
  width: 0%;
  background: var(--primary);
  border-radius: 99px;
  transition: width 0.4s ease;
}

/* ── Card ───────────────────────────────────────────────────────────────── */
.card-wrap {
  flex: 1;
  display: flex;
  align-items: center;
  perspective: 1200px;
  padding: 0.5rem 0;
}

.card {
  width: 100%;
  height: 100%;
  min-height: 280px;
  cursor: pointer;
  user-select: none;
  outline: none;
}

.card:focus-visible .card-inner {
  box-shadow: 0 0 0 3px var(--primary);
  border-radius: var(--radius-lg);
}

.card-inner {
  width: 100%;
  height: 100%;
  min-height: 280px;
  position: relative;
  transform-style: preserve-3d;
  transition: transform 0.45s cubic-bezier(0.4, 0, 0.2, 1);
}

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

.card-front,
.card-back {
  position: absolute;
  inset: 0;
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
  background: var(--surface);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 2rem;
  gap: 0.75rem;
}

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

.card-text {
  font-size: 1.875rem;
  font-weight: 700;
  text-align: center;
  color: var(--text);
  line-height: 1.3;
}

.card-notes {
  font-size: 0.9375rem;
  color: var(--muted);
  text-align: center;
  font-style: italic;
  line-height: 1.5;
}

.card-hint {
  position: absolute;
  bottom: 1.25rem;
  font-size: 0.8125rem;
  color: var(--muted);
  font-weight: 500;
  letter-spacing: 0.01em;
}

/* ── Answer Buttons ─────────────────────────────────────────────────────── */
.answer-buttons {
  display: flex;
  gap: 0.75rem;
  padding-bottom: 0.5rem;
  visibility: hidden;
  pointer-events: none;
}

.answer-buttons.visible {
  visibility: visible;
  pointer-events: auto;
}

.btn-miss {
  flex: 1;
  background: var(--miss-dim);
  color: var(--miss);
  border: 2px solid transparent;
}

.btn-miss:hover {
  opacity: 0.85;
}

.btn-know {
  flex: 1;
  background: var(--know-dim);
  color: var(--know);
  border: 2px solid transparent;
}

.btn-know:hover {
  opacity: 0.85;
}

/* ── Recent decks label ─────────────────────────────────────────────────── */
.recent-label {
  font-size: 0.8125rem;
  font-weight: 600;
  color: var(--muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-top: 0.25rem;
}

/* ── Summary Screen ─────────────────────────────────────────────────────── */
.summary-title {
  font-size: 1.5rem;
  font-weight: 800;
  letter-spacing: -0.5px;
}

.summary-score-wrap {
  background: var(--primary-dim);
  border-radius: var(--radius-lg);
  padding: 2rem;
  text-align: center;
  display: flex;
  flex-direction: column;
  gap: 0.25rem;
}

.summary-score-num {
  font-size: 3rem;
  font-weight: 800;
  color: var(--primary);
  letter-spacing: -1px;
  line-height: 1;
}

.summary-score-label {
  font-size: 0.9375rem;
  color: var(--muted);
  font-weight: 500;
}