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

:root {
  --bg:        #f0f4f8;
  --surface:   #ffffff;
  --surface2:  #e8eef4;
  --border:    #d1dbe6;
  --text:      #1a2533;
  --text-mute: #6b7a8d;
  --primary:   #4a7fd4;
  --primary-h: #3a6fc4;

  --grade1: #e74c3c;
  --grade2: #e67e22;
  --grade3: #27ae60;
  --grade4: #3498db;

  --badge-new:        #9b59b6;
  --badge-learning:   #e67e22;
  --badge-relearning: #e74c3c;
  --badge-review:     #27ae60;

  --radius:  14px;
  --shadow:  0 4px 20px rgba(0,0,0,.10);
  --trans:   .2s ease;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg:        #111827;
    --surface:   #1f2937;
    --surface2:  #273040;
    --border:    #374151;
    --text:      #f3f4f6;
    --text-mute: #9ca3af;
    --primary:   #60a5fa;
    --primary-h: #3b82f6;
    --shadow:    0 4px 20px rgba(0,0,0,.40);
  }
}

/* ── Base ───────────────────────────────────────────────────────────────────── */
html, body {
  height: 100%;
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
}

button {
  font-family: inherit;
  cursor: pointer;
  border: none;
  outline: none;
}

button:focus-visible { outline: 3px solid var(--primary); outline-offset: 2px; }

/* ── Screens ────────────────────────────────────────────────────────────────── */
.screen { min-height: 100dvh; }
[hidden] { display: none !important; }

/* ── Login screen ───────────────────────────────────────────────────────────── */
#screen-login {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 1.5rem;
  padding: 2rem;
  text-align: center;
}

.login-card {
  background: var(--surface);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 2.5rem 2rem;
  max-width: 360px;
  width: 100%;
}

.login-card .flag { font-size: 3rem; margin-bottom: .5rem; }
.login-card h1    { font-size: 1.5rem; font-weight: 700; margin-bottom: .25rem; }
.login-card p     { color: var(--text-mute); font-size: .9rem; margin-bottom: 1.75rem; }

#btn-login {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: .65rem;
  width: 100%;
  padding: .85rem 1.25rem;
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 10px;
  font-size: 1rem;
  font-weight: 600;
  color: var(--text);
  transition: background var(--trans), box-shadow var(--trans);
}
#btn-login:hover { background: var(--border); box-shadow: var(--shadow); }

.google-icon { width: 20px; height: 20px; }

/* ── App shell ──────────────────────────────────────────────────────────────── */
#screen-app {
  display: flex;
  flex-direction: column;
  height: 100dvh;
  max-width: 540px;
  margin: 0 auto;
}

/* ── Top header ─────────────────────────────────────────────────────────────── */
.app-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: .75rem 1rem;
  background: var(--surface);
  border-bottom: 1px solid var(--border);
  flex-shrink: 0;
}

.app-header .brand { font-weight: 700; font-size: 1rem; letter-spacing: -.01em; }

.session-stats {
  display: flex;
  gap: 1rem;
  font-size: .8rem;
  color: var(--text-mute);
}

.user-area {
  display: flex;
  align-items: center;
  gap: .5rem;
}

#user-avatar {
  width: 28px; height: 28px;
  border-radius: 50%;
  object-fit: cover;
}

#btn-logout {
  font-size: .75rem;
  color: var(--text-mute);
  background: none;
  padding: .2rem .5rem;
  border-radius: 6px;
  transition: background var(--trans);
}
#btn-logout:hover { background: var(--surface2); }

/* ── Views ──────────────────────────────────────────────────────────────────── */
.view {
  flex: 1;
  overflow-y: auto;
  padding: 1.25rem 1rem;
  display: flex;
  flex-direction: column;
}

/* ── Study view ─────────────────────────────────────────────────────────────── */
#view-study { align-items: center; gap: 1.25rem; }

/* 3-D flip card container */
.card-scene {
  perspective: 900px;
  width: 100%;
  max-width: 480px;
}

.card-box {
  position: relative;
  width: 100%;
  min-height: 220px;
  transform-style: preserve-3d;
  transition: transform .45s cubic-bezier(.4,0,.2,1);
}

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

.card-face {
  position: absolute;
  inset: 0;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: .75rem;
  padding: 2rem 1.5rem;
  background: var(--surface);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
  min-height: 220px;
}

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

#card-greek {
  font-size: clamp(1.7rem, 6vw, 2.4rem);
  font-weight: 700;
  text-align: center;
  line-height: 1.25;
}

#card-greek-back {
  font-size: clamp(1rem, 3.5vw, 1.3rem);
  font-weight: 600;
  text-align: center;
  color: var(--text-mute);
}

#card-translation {
  font-size: clamp(1.4rem, 5vw, 2rem);
  font-weight: 700;
  text-align: center;
}

/* Badges */
.badge {
  font-size: .7rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: .06em;
  padding: .2rem .6rem;
  border-radius: 99px;
  color: #fff;
  position: absolute;
  top: .75rem;
  right: .85rem;
}
.badge-new        { background: var(--badge-new); }
.badge-learning   { background: var(--badge-learning); }
.badge-relearning { background: var(--badge-relearning); }
.badge-review     { background: var(--badge-review); }

/* ── Reveal button ──────────────────────────────────────────────────────────── */
#btn-reveal {
  width: 100%;
  max-width: 480px;
  padding: .9rem;
  background: var(--primary);
  color: #fff;
  border-radius: var(--radius);
  font-size: 1rem;
  font-weight: 600;
  transition: background var(--trans), transform var(--trans);
}
#btn-reveal:hover  { background: var(--primary-h); transform: translateY(-1px); }
#btn-reveal:active { transform: translateY(0); }

.key-hint {
  font-size: .75rem;
  opacity: .75;
  font-weight: 400;
}

/* ── Rating buttons ─────────────────────────────────────────────────────────── */
#rating-row {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: .5rem;
  width: 100%;
  max-width: 480px;
}

.grade-btn {
  display: flex;
  flex-direction: column;
  align-items: center;
  padding: .7rem .4rem;
  border-radius: var(--radius);
  color: #fff;
  font-weight: 700;
  transition: filter var(--trans), transform var(--trans);
  gap: .2rem;
}
.grade-btn:hover  { filter: brightness(1.1); transform: translateY(-2px); }
.grade-btn:active { transform: translateY(0); }

.grade-btn .label { font-size: .95rem; }
.grade-btn .key   { font-size: .75rem; opacity: .8; }
.grade-btn .hint  { font-size: .7rem; opacity: .75; min-height: .9rem; }

.grade-btn[data-grade="1"] { background: var(--grade1); }
.grade-btn[data-grade="2"] { background: var(--grade2); }
.grade-btn[data-grade="3"] { background: var(--grade3); }
.grade-btn[data-grade="4"] { background: var(--grade4); }

/* ── Keyboard shortcut legend ───────────────────────────────────────────────── */
.shortcut-legend {
  font-size: .75rem;
  color: var(--text-mute);
  text-align: center;
}
kbd {
  display: inline-block;
  padding: .1rem .35rem;
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 4px;
  font-family: monospace;
  font-size: .75rem;
}

/* ── Done view ──────────────────────────────────────────────────────────────── */
#view-done {
  align-items: center;
  justify-content: center;
  text-align: center;
  gap: 1rem;
}

.done-trophy { font-size: 4rem; }
#view-done h2 { font-size: 1.6rem; font-weight: 700; }

.done-stats {
  background: var(--surface);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 1.25rem 1.5rem;
  width: 100%;
  max-width: 360px;
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: .75rem 1.5rem;
}

.done-stat { text-align: center; }
.done-stat .val { font-size: 2rem; font-weight: 800; color: var(--primary); }
.done-stat .lbl { font-size: .8rem; color: var(--text-mute); }

#done-breakdown {
  font-size: .85rem;
  color: var(--text-mute);
}

#btn-restart {
  padding: .85rem 2rem;
  background: var(--primary);
  color: #fff;
  border-radius: var(--radius);
  font-size: 1rem;
  font-weight: 600;
  transition: background var(--trans);
}
#btn-restart:hover { background: var(--primary-h); }

/* ── Progress view ──────────────────────────────────────────────────────────── */
#view-progress { gap: 1rem; }

#view-progress h2 { font-size: 1.25rem; font-weight: 700; }

.progress-bar-wrap {
  background: var(--surface2);
  border-radius: 99px;
  height: 12px;
  overflow: hidden;
  width: 100%;
}

#prog-fill {
  height: 100%;
  background: var(--primary);
  border-radius: 99px;
  transition: width .5s ease;
}

.prog-label {
  display: flex;
  justify-content: space-between;
  font-size: .85rem;
  color: var(--text-mute);
}

.stats-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: .75rem;
}

.stat-card {
  background: var(--surface);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 1rem .75rem;
  text-align: center;
}
.stat-card .val { font-size: 1.75rem; font-weight: 800; }
.stat-card .lbl { font-size: .75rem; color: var(--text-mute); margin-top: .1rem; }

.stat-card.new        .val { color: var(--badge-new); }
.stat-card.learning   .val { color: var(--badge-learning); }
.stat-card.review     .val { color: var(--badge-review); }
.stat-card.due        .val { color: var(--primary); }
.stat-card.total      .val { color: var(--text); }

.info-card {
  background: var(--surface);
  border-radius: var(--radius);
  padding: 1rem 1.1rem;
  font-size: .9rem;
}
.info-card .row { display: flex; justify-content: space-between; padding: .3rem 0; border-bottom: 1px solid var(--border); }
.info-card .row:last-child { border-bottom: none; }
.info-card .row .lbl { color: var(--text-mute); }
.info-card .row .val { font-weight: 600; }

/* ── Bottom tabs ────────────────────────────────────────────────────────────── */
.tab-bar {
  display: flex;
  background: var(--surface);
  border-top: 1px solid var(--border);
  flex-shrink: 0;
}

.tab {
  flex: 1;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: .2rem;
  padding: .6rem .5rem;
  background: none;
  color: var(--text-mute);
  font-size: .7rem;
  font-weight: 500;
  transition: color var(--trans), background var(--trans);
  border-top: 2px solid transparent;
}

.tab .icon { font-size: 1.35rem; line-height: 1; }
.tab.active { color: var(--primary); border-top-color: var(--primary); }
.tab:hover:not(.active) { background: var(--surface2); }

/* ── Toast ──────────────────────────────────────────────────────────────────── */
#toast {
  position: fixed;
  bottom: 5rem;
  left: 50%;
  transform: translateX(-50%);
  background: #1a2533;
  color: #fff;
  padding: .65rem 1.25rem;
  border-radius: 99px;
  font-size: .85rem;
  box-shadow: 0 4px 16px rgba(0,0,0,.25);
  z-index: 999;
  pointer-events: none;
}

/* ── Responsive tweaks ──────────────────────────────────────────────────────── */
@media (min-width: 480px) {
  .stats-grid { grid-template-columns: repeat(5, 1fr); }
  #rating-row { gap: .75rem; }
  .grade-btn  { padding: .9rem .5rem; }
}