:root {
  --bg: #0f1419;
  --surface: #1a2332;
  --surface-2: #243044;
  --border: #2d3a4f;
  --text: #e8edf4;
  --text-muted: #8b9cb3;
  --accent: #6c9eff;
  --accent-hover: #8bb4ff;
  --success: #34d399;
  --error: #f87171;
  --radius: 12px;
  --shadow: 0 4px 24px rgba(0, 0, 0, 0.35);
}

*, *::before, *::after { box-sizing: border-box; }

body {
  margin: 0;
  min-height: 100vh;
  font-family: "Segoe UI", "PingFang SC", "Microsoft YaHei", sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
}

.header {
  background: var(--surface);
  border-bottom: 1px solid var(--border);
  padding: 1.25rem 1.5rem 0;
}

.header-inner { margin-bottom: 1rem; }

.header h1 {
  margin: 0;
  font-size: 1.5rem;
  font-weight: 600;
}

.subtitle {
  margin: 0.25rem 0 0;
  color: var(--text-muted);
  font-size: 0.875rem;
}

.nav {
  display: flex;
  gap: 0.25rem;
  flex-wrap: wrap;
}

.nav-btn {
  background: none;
  border: none;
  color: var(--text-muted);
  padding: 0.625rem 1rem;
  cursor: pointer;
  font-size: 0.9375rem;
  border-bottom: 2px solid transparent;
  transition: color 0.15s, border-color 0.15s;
}

.nav-btn:hover { color: var(--text); }

.nav-btn.active {
  color: var(--accent);
  border-bottom-color: var(--accent);
}

.main {
  max-width: 960px;
  margin: 0 auto;
  padding: 1.5rem;
}

.tab-panel { display: none; }
.tab-panel.active { display: block; }

.panel-grid {
  display: grid;
  gap: 1.25rem;
}

@media (min-width: 720px) {
  .panel-grid {
    grid-template-columns: 280px 1fr;
  }
}

.card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem;
  box-shadow: var(--shadow);
}

.card-wide { grid-column: 1 / -1; }

@media (min-width: 720px) {
  .card-wide { grid-column: 2; }
}

.card h2 {
  margin: 0 0 1rem;
  font-size: 1.0625rem;
  font-weight: 600;
}

.color-picker-row {
  display: flex;
  align-items: center;
  gap: 1rem;
  margin-bottom: 1rem;
}

.color-picker-row input[type="color"] {
  width: 56px;
  height: 56px;
  border: 2px solid var(--border);
  border-radius: 8px;
  cursor: pointer;
  padding: 2px;
  background: var(--surface-2);
}

.color-info {
  display: flex;
  flex-direction: column;
  gap: 0.125rem;
  font-family: "Cascadia Code", "Consolas", monospace;
  font-size: 0.875rem;
}

#base-hex { font-weight: 600; }
#base-hsl { color: var(--text-muted); font-size: 0.8125rem; }

#color-wheel {
  display: block;
  margin: 0 auto 1rem;
  cursor: crosshair;
  border-radius: 50%;
}

.slider-group {
  margin-bottom: 0.75rem;
}

.slider-group label {
  display: flex;
  justify-content: space-between;
  font-size: 0.875rem;
  color: var(--text-muted);
  margin-bottom: 0.375rem;
}

.slider-group input[type="range"] {
  width: 100%;
  accent-color: var(--accent);
}

.scheme-tabs, .quiz-type-tabs {
  display: flex;
  flex-wrap: wrap;
  gap: 0.375rem;
  margin-bottom: 1rem;
}

.scheme-btn, .quiz-type-btn {
  background: var(--surface-2);
  border: 1px solid var(--border);
  color: var(--text-muted);
  padding: 0.375rem 0.75rem;
  border-radius: 6px;
  cursor: pointer;
  font-size: 0.8125rem;
  transition: background 0.15s, color 0.15s, border-color 0.15s;
}

.scheme-btn:hover, .quiz-type-btn:hover {
  color: var(--text);
  border-color: var(--accent);
}

.scheme-btn.active, .quiz-type-btn.active {
  background: var(--accent);
  color: #0f1419;
  border-color: var(--accent);
  font-weight: 600;
}

.scheme-desc {
  color: var(--text-muted);
  font-size: 0.875rem;
  margin: 0 0 1rem;
  min-height: 2.5em;
}

.palette {
  display: flex;
  gap: 0.5rem;
  flex-wrap: wrap;
  margin-bottom: 1rem;
}

.swatch {
  flex: 1;
  min-width: 72px;
  height: 96px;
  border-radius: 8px;
  border: 2px solid rgba(255, 255, 255, 0.1);
  cursor: pointer;
  transition: transform 0.15s;
  position: relative;
}

.swatch:hover { transform: scale(1.04); }

.swatch-label {
  position: absolute;
  bottom: 6px;
  left: 0;
  right: 0;
  text-align: center;
  font-size: 0.6875rem;
  font-family: monospace;
  text-shadow: 0 1px 3px rgba(0, 0, 0, 0.8);
}

.palette-codes {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.code-chip {
  background: var(--surface-2);
  border: 1px solid var(--border);
  padding: 0.25rem 0.625rem;
  border-radius: 4px;
  font-family: monospace;
  font-size: 0.8125rem;
  cursor: pointer;
}

.code-chip:hover { border-color: var(--accent); }

/* Quiz */
.quiz-card { max-width: 640px; margin: 0 auto; }

.quiz-header {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  flex-wrap: wrap;
  gap: 0.75rem;
  margin-bottom: 1rem;
}

.quiz-meta {
  display: flex;
  gap: 1rem;
  font-size: 0.875rem;
  color: var(--text-muted);
}

.quiz-content { margin-bottom: 1rem; }

.quiz-palette {
  display: flex;
  gap: 0.5rem;
  margin: 1rem 0;
}

.quiz-palette .swatch {
  flex: 1;
  min-width: 60px;
  height: 80px;
  cursor: default;
}

.quiz-options {
  display: grid;
  gap: 0.5rem;
}

.quiz-option {
  background: var(--surface-2);
  border: 2px solid var(--border);
  color: var(--text);
  padding: 0.75rem 1rem;
  border-radius: 8px;
  cursor: pointer;
  text-align: left;
  font-size: 0.9375rem;
  transition: border-color 0.15s, background 0.15s;
}

.quiz-option:hover:not(:disabled) {
  border-color: var(--accent);
}

.quiz-option:disabled { cursor: default; opacity: 0.7; }

.quiz-option.correct {
  border-color: var(--success);
  background: rgba(52, 211, 153, 0.12);
}

.quiz-option.wrong {
  border-color: var(--error);
  background: rgba(248, 113, 113, 0.12);
}

.color-options {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(72px, 1fr));
  gap: 0.5rem;
}

.color-option {
  height: 72px;
  border: 3px solid rgba(255, 255, 255, 0.35);
  border-radius: 8px;
  cursor: pointer;
  position: relative;
  transition: transform 0.15s, box-shadow 0.15s, border-color 0.15s;
}

.color-option:hover:not(:disabled) { transform: scale(1.05); }

.color-option:disabled { cursor: default; }

.color-option.correct {
  border-color: #fff;
  box-shadow: 0 0 0 3px var(--success);
}

.color-option.correct::after {
  content: '✓';
  position: absolute;
  top: 4px;
  right: 4px;
  width: 22px;
  height: 22px;
  border-radius: 50%;
  background: var(--success);
  color: #0f1419;
  font-size: 14px;
  font-weight: 700;
  line-height: 22px;
  text-align: center;
  box-shadow: 0 1px 4px rgba(0, 0, 0, 0.45);
  pointer-events: none;
}

.color-option.wrong {
  border-color: #fff;
  box-shadow: 0 0 0 3px var(--error);
}

.color-option.wrong::after {
  content: '✕';
  position: absolute;
  top: 4px;
  right: 4px;
  width: 22px;
  height: 22px;
  border-radius: 50%;
  background: var(--error);
  color: #fff;
  font-size: 13px;
  font-weight: 700;
  line-height: 22px;
  text-align: center;
  box-shadow: 0 1px 4px rgba(0, 0, 0, 0.45);
  pointer-events: none;
}

.quiz-feedback {
  padding: 0.75rem 1rem;
  border-radius: 8px;
  margin-bottom: 1rem;
  font-size: 0.9375rem;
}

.quiz-feedback.success {
  background: rgba(52, 211, 153, 0.12);
  border: 1px solid var(--success);
  color: var(--success);
}

.quiz-feedback.error {
  background: rgba(248, 113, 113, 0.12);
  border: 1px solid var(--error);
  color: var(--error);
}

.hidden { display: none !important; }

.btn {
  border: none;
  padding: 0.625rem 1.25rem;
  border-radius: 8px;
  font-size: 0.9375rem;
  cursor: pointer;
  transition: background 0.15s;
}

.btn-primary {
  background: var(--accent);
  color: #0f1419;
  font-weight: 600;
}

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

.btn-danger {
  background: transparent;
  border: 1px solid var(--error);
  color: var(--error);
  margin-top: 1rem;
}

.btn-danger:hover { background: rgba(248, 113, 113, 0.1); }

/* Contrast */
.contrast-pickers {
  display: flex;
  flex-direction: column;
  gap: 1.25rem;
}

.contrast-pickers label {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
  font-size: 0.875rem;
  color: var(--text-muted);
}

.contrast-pickers input[type="color"] {
  width: 100%;
  height: 48px;
  border: 2px solid var(--border);
  border-radius: 8px;
  cursor: pointer;
}

.contrast-preview {
  padding: 2rem;
  border-radius: 8px;
  margin-bottom: 1rem;
  text-align: center;
}

.preview-text {
  margin: 0;
  font-size: 1.5rem;
  font-weight: 600;
}

.contrast-results {
  display: grid;
  gap: 0.75rem;
}

.contrast-row {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 0.75rem 1rem;
  background: var(--surface-2);
  border-radius: 8px;
  font-size: 0.9375rem;
}

.contrast-row .pass { color: var(--success); font-weight: 600; }
.contrast-row .fail { color: var(--error); font-weight: 600; }

.hint {
  color: var(--text-muted);
  font-size: 0.8125rem;
  margin: 0.75rem 0 0;
}

/* Progress */
.progress-stats {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(140px, 1fr));
  gap: 0.75rem;
  margin-bottom: 1.5rem;
}

.stat-box {
  background: var(--surface-2);
  border-radius: 8px;
  padding: 1rem;
  text-align: center;
}

.stat-value {
  font-size: 1.75rem;
  font-weight: 700;
  color: var(--accent);
}

.stat-label {
  font-size: 0.8125rem;
  color: var(--text-muted);
  margin-top: 0.25rem;
}

.progress-history h3 {
  font-size: 0.9375rem;
  margin: 0 0 0.75rem;
}

.history-list {
  list-style: none;
  padding: 0;
  margin: 0;
  max-height: 240px;
  overflow-y: auto;
}

.history-list li {
  padding: 0.5rem 0;
  border-bottom: 1px solid var(--border);
  font-size: 0.8125rem;
  color: var(--text-muted);
  display: flex;
  justify-content: space-between;
  gap: 0.5rem;
}

.history-list .result-correct { color: var(--success); }
.history-list .result-wrong { color: var(--error); }

.footer {
  max-width: 960px;
  margin: 2rem auto 1.5rem;
  padding: 0 1.5rem;
  display: flex;
  justify-content: space-between;
  font-size: 0.75rem;
  color: var(--text-muted);
}