/* ═══════════════════════════════════════════════════════════════
   Assertive Tech English — Apple HIG Design System
   Zero-framework, CSS Custom Properties only
   ═══════════════════════════════════════════════════════════════ */

/* ── Design Tokens (Light) ── */
:root {
  --apple-bg: #f5f5f7;
  --apple-surface: rgba(255, 255, 255, 0.82);
  --apple-border: rgba(0, 0, 0, 0.08);
  --apple-text-primary: #1d1d1f;
  --apple-text-secondary: #86868b;
  --apple-text-tertiary: #aeaeb2;
  --apple-blue: #0071e3;
  --apple-green: #34c759;
  --apple-orange: #ff9500;
  --apple-red: #ff3b30;
  --apple-purple: #af52de;
  --apple-teal: #5ac8fa;
  --apple-blur: blur(20px) saturate(180%);
  --apple-card-shadow: 0 4px 24px -2px rgba(0, 0, 0, 0.06), 0 1px 2px rgba(0, 0, 0, 0.04);
  --apple-focus-ring: 0 0 0 4px rgba(0, 113, 227, 0.35);
  --radius: 14px;
  --radius-sm: 8px;
  --font-ui: -apple-system, BlinkMacSystemFont, "SF Pro Display", "SF Pro Text", system-ui, sans-serif;
  --font-serif: "New York", Georgia, "Times New Roman", serif;
  --font-mono: "SF Mono", Menlo, "Cascadia Code", monospace;
}

/* ── Dark Mode ── */
@media (prefers-color-scheme: dark) {
  :root {
    --apple-bg: #000000;
    --apple-surface: rgba(28, 28, 30, 0.78);
    --apple-border: rgba(255, 255, 255, 0.12);
    --apple-text-primary: #f5f5f7;
    --apple-text-secondary: #86868b;
    --apple-text-tertiary: #636366;
    --apple-blue: #2997ff;
    --apple-card-shadow: 0 8px 32px 0 rgba(0, 0, 0, 0.37);
  }
}

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

html { font-size: 16px; -webkit-font-smoothing: antialiased; }

body {
  font-family: var(--font-ui);
  background: var(--apple-bg);
  color: var(--apple-text-primary);
  min-height: 100vh;
  line-height: 1.6;
}

/* ── Nav Bar ── */
.nav-bar {
  position: sticky; top: 0; z-index: 100;
  display: flex; align-items: center; justify-content: space-between;
  padding: 12px 24px;
  background: var(--apple-surface);
  backdrop-filter: var(--apple-blur);
  -webkit-backdrop-filter: var(--apple-blur);
  border-bottom: 1px solid var(--apple-border);
}
.nav-brand { font-weight: 700; font-size: 1.1rem; letter-spacing: -0.02em; }
.nav-links { display: flex; gap: 4px; }
.nav-btn {
  font-family: var(--font-ui);
  font-size: 0.875rem; font-weight: 500;
  padding: 6px 14px; border-radius: 8px;
  border: none; cursor: pointer;
  color: var(--apple-text-secondary);
  background: transparent;
  transition: all 0.2s cubic-bezier(0.16, 1, 0.3, 1);
}
.nav-btn:hover { background: var(--apple-border); }
.nav-btn.active { color: var(--apple-blue); background: rgba(0, 113, 227, 0.08); }

/* ── Views ── */
.view { display: none; max-width: 720px; margin: 0 auto; padding: 32px 20px; }
.view.active { display: block; }

/* ── Card ── */
.card {
  background: var(--apple-surface);
  backdrop-filter: var(--apple-blur);
  -webkit-backdrop-filter: var(--apple-blur);
  border-radius: var(--radius);
  border: 1px solid var(--apple-border);
  box-shadow: var(--apple-card-shadow);
  padding: 24px;
  transition: transform 0.3s cubic-bezier(0.16, 1, 0.3, 1);
}

.card-header {
  display: flex; align-items: center; gap: 12px; flex-wrap: wrap;
  margin-bottom: 20px; font-size: 0.85rem;
  color: var(--apple-text-secondary);
}

.badge {
  display: inline-block;
  padding: 2px 10px; border-radius: 20px;
  font-size: 0.75rem; font-weight: 600; letter-spacing: 0.02em;
  background: rgba(0, 113, 227, 0.1);
  color: var(--apple-blue);
}

/* ── Hint ── */
.card-hint { margin-bottom: 20px; }
.hint-label {
  font-size: 0.8rem; font-weight: 600;
  color: var(--apple-text-secondary);
  margin-bottom: 8px;
  text-transform: uppercase; letter-spacing: 0.04em;
}
.hint-text {
  font-family: var(--font-ui);
  font-size: 1rem; line-height: 1.7;
  color: var(--apple-text-primary);
}

/* ── Input Area ── */
.card-input-area { margin-bottom: 20px; }
.blind-textarea {
  width: 100%;
  font-family: var(--font-mono);
  font-size: 0.95rem; line-height: 1.6;
  padding: 14px 16px;
  background: var(--apple-bg);
  border: 1px solid var(--apple-border);
  border-radius: var(--radius-sm);
  color: var(--apple-text-primary);
  resize: vertical;
  transition: border-color 0.2s, box-shadow 0.2s;
}
.blind-textarea:focus {
  outline: none;
  border-color: var(--apple-blue);
  box-shadow: var(--apple-focus-ring);
}

/* ── Cloze ── */
.cloze-text {
  font-family: var(--font-mono);
  font-size: 1rem; line-height: 2;
  padding: 14px 16px;
  background: var(--apple-bg);
  border-radius: var(--radius-sm);
  border: 1px solid var(--apple-border);
}
.cloze-text .cloze-blank {
  display: inline-block;
  min-width: 80px;
  border-bottom: 2px dashed var(--apple-teal);
  color: transparent;
  background: rgba(90, 200, 250, 0.08);
  border-radius: 4px;
  padding: 0 6px; margin: 0 2px;
  position: relative;
  cursor: pointer;
}
.cloze-text .cloze-blank.revealed {
  color: var(--apple-teal);
  border-bottom-style: solid;
}

/* ── Diff ── */
.diff-result { margin-bottom: 20px; }
.diff-output {
  font-family: var(--font-mono);
  font-size: 0.95rem; line-height: 2;
  padding: 14px 16px;
  background: var(--apple-bg);
  border-radius: var(--radius-sm);
  border: 1px solid var(--apple-border);
  word-break: break-word;
}
.diff-output .diff-correct { color: var(--apple-green); }
.diff-output .diff-wrong { color: var(--apple-red); text-decoration: line-through; }
.diff-output .diff-missing { color: var(--apple-red); opacity: 0.6; font-style: italic; }
.diff-output .diff-extra { color: var(--apple-orange); text-decoration: wavy underline; }
.diff-score {
  margin-top: 8px; font-size: 0.9rem; font-weight: 600;
  color: var(--apple-text-secondary);
}
.diff-score.pass { color: var(--apple-green); }
.diff-score.fail { color: var(--apple-red); }

/* ── Rating Buttons ── */
.rating-buttons {
  display: grid; grid-template-columns: repeat(4, 1fr); gap: 8px;
}
.rate-btn {
  font-family: var(--font-ui);
  font-size: 0.85rem; font-weight: 600;
  padding: 12px 8px;
  border-radius: var(--radius-sm);
  border: 1px solid var(--apple-border);
  cursor: pointer;
  transition: all 0.2s cubic-bezier(0.16, 1, 0.3, 1);
  background: var(--apple-surface);
  color: var(--apple-text-primary);
}
.rate-btn:hover { transform: translateY(-1px); box-shadow: var(--apple-card-shadow); }
.rate-btn kbd {
  display: inline-block; font-family: var(--font-mono);
  font-size: 0.75rem; padding: 1px 5px; margin-right: 4px;
  border-radius: 4px; background: var(--apple-bg);
  border: 1px solid var(--apple-border);
}
.rate-again:hover { border-color: var(--apple-red); }
.rate-hard:hover  { border-color: var(--apple-orange); }
.rate-good:hover  { border-color: var(--apple-green); }
.rate-easy:hover  { border-color: var(--apple-blue); }

/* ── Empty State ── */
.empty-state {
  text-align: center; padding: 80px 20px;
  color: var(--apple-text-secondary);
}
.empty-icon { font-size: 3rem; margin-bottom: 12px; }

/* ── BYOB ── */
.byob-container { max-width: 640px; }
.field-label {
  display: block; margin: 16px 0 6px;
  font-size: 0.8rem; font-weight: 600;
  color: var(--apple-text-secondary);
  text-transform: uppercase; letter-spacing: 0.04em;
}
.input {
  width: 100%;
  font-family: var(--font-ui);
  font-size: 0.95rem;
  padding: 10px 14px;
  background: var(--apple-bg);
  border: 1px solid var(--apple-border);
  border-radius: var(--radius-sm);
  color: var(--apple-text-primary);
  transition: border-color 0.2s, box-shadow 0.2s;
}
.input:focus {
  outline: none;
  border-color: var(--apple-blue);
  box-shadow: var(--apple-focus-ring);
}
.textarea { resize: vertical; font-family: var(--font-mono); line-height: 1.6; }

.btn-primary {
  display: inline-block;
  margin-top: 16px; padding: 12px 28px;
  font-family: var(--font-ui);
  font-size: 0.9rem; font-weight: 600;
  color: #fff; background: var(--apple-blue);
  border: none; border-radius: 980px;
  cursor: pointer;
  transition: all 0.2s cubic-bezier(0.16, 1, 0.3, 1);
}
.btn-primary:hover { filter: brightness(1.1); transform: scale(1.02); }
.btn-primary:disabled { opacity: 0.5; cursor: not-allowed; transform: none; }

.btn-secondary {
  display: inline-block;
  margin-top: 8px; margin-right: 8px;
  padding: 10px 20px;
  font-family: var(--font-ui);
  font-size: 0.85rem; font-weight: 500;
  color: var(--apple-blue);
  background: rgba(0, 113, 227, 0.08);
  border: none; border-radius: 980px;
  cursor: pointer;
  transition: all 0.2s;
}
.btn-secondary:hover { background: rgba(0, 113, 227, 0.14); }

.byob-status {
  margin-top: 12px;
  font-size: 0.85rem;
  color: var(--apple-text-secondary);
  white-space: pre-wrap;
}
.byob-status.error { color: var(--apple-red); }

/* ── Settings ── */
.settings-container { max-width: 480px; }
.divider { border: none; border-top: 1px solid var(--apple-border); margin: 28px 0; }

/* ── Fuse bar (25 min timer) ── */
.fuse-bar {
  position: fixed; bottom: 0; left: 0; right: 0;
  height: 4px;
  background: var(--apple-border);
  z-index: 200;
}
.fuse-fill {
  height: 100%; width: 0%;
  background: linear-gradient(90deg, var(--apple-green), var(--apple-orange), var(--apple-red));
  transition: width 1s linear;
}
.fuse-bar span {
  position: absolute; right: 12px; top: -22px;
  font-size: 0.75rem; font-weight: 600;
  color: var(--apple-text-secondary);
}

/* ── BYOB Preview Cards ── */
#byob-cards .preview-card {
  background: var(--apple-bg);
  border: 1px solid var(--apple-border);
  border-radius: var(--radius-sm);
  padding: 14px; margin: 10px 0;
  font-size: 0.9rem;
}
#byob-cards .preview-card .pc-level {
  font-size: 0.75rem; font-weight: 700;
  color: var(--apple-teal);
  text-transform: uppercase;
  margin-bottom: 6px;
}
#byob-cards .preview-card .pc-en {
  font-family: var(--font-mono);
  line-height: 1.6; margin-bottom: 6px;
}
#byob-cards .preview-card .pc-zh {
  color: var(--apple-text-secondary);
  font-size: 0.85rem;
}

/* ── Utilities ── */
.text-secondary { color: var(--apple-text-secondary); }

/* ── Responsive ── */
@media (max-width: 600px) {
  .nav-bar { padding: 10px 14px; }
  .view { padding: 20px 14px; }
  .rating-buttons { grid-template-columns: repeat(2, 1fr); }
}