/* ===== 设计令牌 ===== */
:root {
  /* 纸张色系 */
  --paper-bg: #F8F5EE;
  --paper-lines: #E8E2D5;
  --paper-grid: #DDD6C6;
  --paper-shadow: rgba(80, 60, 30, 0.08);

  /* 墨水色系 */
  --ink-primary: #1F2937;
  --ink-secondary: #4B5563;
  --ink-muted: #6B7280;
  --ink-light: #9CA3AF;

  /* 教学主题色 */
  --math-blue: #2563EB;
  --math-blue-light: #DBEAFE;
  --math-red: #DC2626;
  --math-red-light: #FEE2E2;
  --math-green: #059669;
  --math-green-light: #D1FAE5;
  --math-amber: #D97706;
  --math-amber-light: #FEF3C7;
  --math-purple: #7C3AED;
  --math-purple-light: #EDE9FE;
  --math-teal: #0D9488;
  --math-teal-light: #CCFBF1;
  --math-pink: #DB2777;
  --math-pink-light: #FCE7F3;

  /* 尺寸 */
  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-lg: 12px;
  --shadow-sm: 0 1px 2px var(--paper-shadow);
  --shadow-md: 0 4px 12px var(--paper-shadow);
  --shadow-lg: 0 8px 24px var(--paper-shadow);
}

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: 'Noto Sans SC', -apple-system, BlinkMacSystemFont, sans-serif;
  background-color: var(--paper-bg);
  color: var(--ink-primary);
  line-height: 1.6;
  min-height: 100vh;
  /* 方格纸背景 */
  background-image:
    linear-gradient(var(--paper-grid) 1px, transparent 1px),
    linear-gradient(90deg, var(--paper-grid) 1px, transparent 1px);
  background-size: 24px 24px;
  background-position: -1px -1px;
}

/* ===== 顶部标题 ===== */
.app-header {
  background: linear-gradient(135deg, #1E3A8A 0%, #2563EB 100%);
  color: white;
  padding: 20px 32px;
  box-shadow: var(--shadow-md);
  position: relative;
  z-index: 10;
}

.app-header h1 {
  font-family: 'Noto Serif SC', serif;
  font-size: 24px;
  font-weight: 700;
  letter-spacing: 1px;
}

.app-header .subtitle {
  font-size: 14px;
  opacity: 0.85;
  margin-top: 4px;
}

.app-header .badge {
  display: inline-block;
  background: rgba(255,255,255,0.2);
  padding: 2px 10px;
  border-radius: 20px;
  font-size: 12px;
  margin-left: 12px;
  vertical-align: middle;
}

/* ===== Tab 导航 ===== */
.tab-nav {
  display: flex;
  background: white;
  border-bottom: 2px solid var(--paper-lines);
  padding: 0 32px;
  gap: 4px;
}

.tab-item {
  padding: 14px 24px;
  cursor: pointer;
  font-size: 15px;
  font-weight: 500;
  color: var(--ink-secondary);
  border-bottom: 3px solid transparent;
  transition: all 0.2s;
  display: flex;
  align-items: center;
  gap: 8px;
  user-select: none;
}

.tab-item:hover {
  color: var(--math-blue);
  background: var(--math-blue-light);
}

.tab-item.active {
  color: var(--math-blue);
  border-bottom-color: var(--math-blue);
  font-weight: 600;
}

.tab-item .tab-num {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 22px;
  height: 22px;
  background: var(--paper-lines);
  border-radius: 50%;
  font-size: 12px;
  font-weight: 700;
}

.tab-item.active .tab-num {
  background: var(--math-blue);
  color: white;
}

/* ===== 主布局 ===== */
.app-main {
  padding: 24px 32px;
  display: grid;
  grid-template-columns: 240px 1fr;
  gap: 20px;
  min-height: calc(100vh - 130px);
}

/* ===== 控制面板 ===== */
.control-panel {
  background: white;
  border-radius: var(--radius-lg);
  padding: 14px 16px;
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--paper-lines);
  height: fit-content;
  position: sticky;
  top: 20px;
  max-width: 260px;
}

.panel-title {
  font-family: 'Noto Serif SC', serif;
  font-size: 14px;
  font-weight: 700;
  color: var(--ink-primary);
  margin-bottom: 10px;
  padding-bottom: 6px;
  border-bottom: 2px solid var(--paper-lines);
  display: flex;
  align-items: center;
  gap: 6px;
}

.panel-title::before {
  content: '';
  width: 3px;
  height: 14px;
  background: var(--math-blue);
  border-radius: 2px;
}

/* 函数输入 */
.func-input-group {
  margin-bottom: 12px;
}

.func-label {
  font-size: 12px;
  color: var(--ink-secondary);
  margin-bottom: 6px;
  font-weight: 500;
}

.func-formula {
  background: var(--paper-bg);
  padding: 8px 10px;
  border-radius: var(--radius-md);
  border: 1px solid var(--paper-lines);
  font-family: 'Times New Roman', 'Noto Serif SC', serif;
  font-size: 16px;
  text-align: center;
  margin-bottom: 10px;
  font-style: italic;
}

.func-formula .var-a { color: var(--math-red); font-weight: 700; }
.func-formula .var-b { color: var(--math-green); font-weight: 700; }
.func-formula .var-c { color: var(--math-blue); font-weight: 700; }

.coeff-row {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr;
  gap: 6px;
  margin-bottom: 8px;
}

.coeff-input {
  display: flex;
  flex-direction: column;
  gap: 3px;
}

.coeff-input label {
  font-size: 11px;
  color: var(--ink-muted);
  font-weight: 500;
}

.coeff-input input[type="number"] {
  padding: 5px 4px;
  border: 1.5px solid var(--paper-lines);
  border-radius: var(--radius-sm);
  font-size: 13px;
  text-align: center;
  font-family: inherit;
  transition: border-color 0.2s;
  width: 100%;
  min-width: 0;
}

.coeff-input input:focus {
  outline: none;
  border-color: var(--math-blue);
}

.coeff-input.a input { border-color: var(--math-red-light); }
.coeff-input.a input:focus { border-color: var(--math-red); }
.coeff-input.b input { border-color: var(--math-green-light); }
.coeff-input.b input:focus { border-color: var(--math-green); }
.coeff-input.c input { border-color: var(--math-blue-light); }
.coeff-input.c input:focus { border-color: var(--math-blue); }

.range-slider {
  width: 100%;
  height: 3px;
  -webkit-appearance: none;
  background: var(--paper-lines);
  border-radius: 2px;
  outline: none;
  padding: 0;
}

.range-slider::-webkit-slider-thumb {
  -webkit-appearance: none;
  width: 13px;
  height: 13px;
  border-radius: 50%;
  background: var(--math-blue);
  cursor: pointer;
  box-shadow: 0 1px 2px rgba(0,0,0,0.2);
}

.coeff-input.a .range-slider::-webkit-slider-thumb { background: var(--math-red); }
.coeff-input.b .range-slider::-webkit-slider-thumb { background: var(--math-green); }
.coeff-input.c .range-slider::-webkit-slider-thumb { background: var(--math-blue); }

.value-display {
  font-size: 11px;
  color: var(--ink-muted);
  text-align: center;
}

/* 按钮 */
.btn {
  padding: 7px 14px;
  border: none;
  border-radius: var(--radius-sm);
  font-size: 13px;
  font-weight: 500;
  cursor: pointer;
  transition: all 0.2s;
  font-family: inherit;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 5px;
}

.btn-primary {
  background: var(--math-blue);
  color: white;
}

.btn-primary:hover {
  background: #1D4ED8;
  transform: translateY(-1px);
}

.btn-secondary {
  background: white;
  color: var(--ink-secondary);
  border: 1.5px solid var(--paper-lines);
}

.btn-secondary:hover {
  border-color: var(--ink-muted);
  color: var(--ink-primary);
}

.btn-danger {
  background: var(--math-red);
  color: white;
}

.btn-danger:hover {
  background: #B91C1C;
}

.btn-success {
  background: var(--math-green);
  color: white;
}

.btn-success:hover {
  background: #047857;
}

.btn-block {
  width: 100%;
}

.btn-sm {
  padding: 5px 12px;
  font-size: 12px;
}

.btn-group {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
}

/* ===== 主展示区 ===== */
.main-area {
  display: flex;
  flex-direction: column;
  gap: 20px;
}

.chart-card {
  background: white;
  border-radius: var(--radius-lg);
  padding: 20px;
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--paper-lines);
}

.chart-card-title {
  font-family: 'Noto Serif SC', serif;
  font-size: 16px;
  font-weight: 700;
  margin-bottom: 12px;
  color: var(--ink-primary);
  display: flex;
  align-items: center;
  gap: 8px;
}

.chart-container {
  width: 100%;
  height: 420px;
  position: relative;
}

/* ===== 步骤指示器 ===== */
.step-nav {
  display: flex;
  gap: 4px;
  margin-bottom: 16px;
  background: var(--paper-bg);
  border-radius: var(--radius-md);
  padding: 4px;
  overflow-x: auto;
}

.step-btn {
  flex: 1;
  min-width: 80px;
  padding: 8px 12px;
  border: none;
  background: transparent;
  border-radius: var(--radius-sm);
  cursor: pointer;
  font-size: 13px;
  font-weight: 500;
  color: var(--ink-secondary);
  transition: all 0.2s;
  font-family: inherit;
  white-space: nowrap;
}

.step-btn:hover {
  background: white;
  color: var(--ink-primary);
}

.step-btn.active {
  background: white;
  color: var(--math-blue);
  box-shadow: var(--shadow-sm);
  font-weight: 600;
}

.step-btn.done {
  color: var(--math-green);
}

.step-btn.done::after {
  content: '✓';
  margin-left: 4px;
  font-size: 12px;
}

/* ===== 答案面板 ===== */
.answer-panel {
  background: var(--math-blue-light);
  border-left: 4px solid var(--math-blue);
  border-radius: var(--radius-sm);
  padding: 14px 18px;
  margin-top: 12px;
  animation: slideDown 0.3s ease;
}

@keyframes slideDown {
  from { opacity: 0; transform: translateY(-8px); }
  to { opacity: 1; transform: translateY(0); }
}

.answer-panel h4 {
  font-size: 14px;
  color: var(--math-blue);
  margin-bottom: 8px;
  display: flex;
  align-items: center;
  gap: 6px;
}

.answer-panel .answer-content {
  font-size: 14px;
  color: var(--ink-primary);
  line-height: 1.8;
}

.answer-panel .answer-content .formula {
  font-family: 'Times New Roman', serif;
  font-style: italic;
  font-size: 16px;
  background: white;
  padding: 2px 8px;
  border-radius: 4px;
  display: inline-block;
  margin: 2px 4px;
}

.answer-panel.hidden-panel {
  display: none;
}

/* ===== 表格样式 ===== */
.data-table {
  width: 100%;
  border-collapse: collapse;
  margin: 10px 0;
  font-size: 14px;
}

.data-table th,
.data-table td {
  border: 1px solid var(--paper-lines);
  padding: 8px 12px;
  text-align: center;
}

.data-table th {
  background: var(--paper-bg);
  font-weight: 600;
  color: var(--ink-secondary);
}

.data-table td {
  font-family: 'Times New Roman', serif;
  font-style: italic;
}

.data-table tr:hover td {
  background: var(--math-blue-light);
}

/* ===== 性质卡片 ===== */
.properties-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: 12px;
  margin: 16px 0;
}

.property-card {
  background: var(--paper-bg);
  border-radius: var(--radius-md);
  padding: 14px 16px;
  border: 1px solid var(--paper-lines);
  transition: all 0.2s;
}

.property-card:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}

.property-card .prop-label {
  font-size: 12px;
  color: var(--ink-muted);
  margin-bottom: 6px;
  display: flex;
  align-items: center;
  gap: 4px;
}

.property-card .prop-value {
  font-size: 15px;
  font-weight: 600;
  color: var(--ink-primary);
}

.property-card .prop-value .formula {
  font-family: 'Times New Roman', serif;
  font-style: italic;
}

.property-card.vertex { border-left: 3px solid var(--math-red); }
.property-card.axis { border-left: 3px solid var(--math-green); }
.property-card.opening { border-left: 3px solid var(--math-blue); }
.property-card.extremum { border-left: 3px solid var(--math-amber); }
.property-card.increase { border-left: 3px solid var(--math-teal); }
.property-card.decrease { border-left: 3px solid var(--math-purple); }
.property-card.y-intercept { border-left: 3px solid var(--math-pink); }

/* ===== 对比探究 ===== */
.compare-list {
  max-height: 240px;
  overflow-y: auto;
  margin: 12px 0;
  border: 1px solid var(--paper-lines);
  border-radius: var(--radius-sm);
}

.compare-item {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 8px 12px;
  border-bottom: 1px solid var(--paper-lines);
  gap: 8px;
}

.compare-item:last-child {
  border-bottom: none;
}

.compare-item:hover {
  background: var(--paper-bg);
}

.color-dot {
  width: 12px;
  height: 12px;
  border-radius: 50%;
  flex-shrink: 0;
}

.compare-item .func-str {
  flex: 1;
  font-family: 'Times New Roman', serif;
  font-style: italic;
  font-size: 14px;
  margin: 0 8px;
  min-width: 0;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.remove-btn {
  background: none;
  border: none;
  color: var(--ink-light);
  cursor: pointer;
  font-size: 16px;
  padding: 2px 6px;
  border-radius: 4px;
}

.remove-btn:hover {
  background: var(--math-red-light);
  color: var(--math-red);
}

.add-btn {
  width: 100%;
  padding: 10px;
  border: 2px dashed var(--paper-lines);
  border-radius: var(--radius-sm);
  background: transparent;
  color: var(--ink-muted);
  cursor: pointer;
  font-size: 14px;
  transition: all 0.2s;
  font-family: inherit;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
}

.add-btn:hover {
  border-color: var(--math-blue);
  color: var(--math-blue);
  background: var(--math-blue-light);
}

/* ===== 对比结论 ===== */
.compare-conclusion {
  background: var(--math-amber-light);
  border-left: 4px solid var(--math-amber);
  border-radius: var(--radius-sm);
  padding: 14px 18px;
  margin-top: 16px;
}

.compare-conclusion h4 {
  font-size: 14px;
  color: #92400E;
  margin-bottom: 8px;
}

.compare-conclusion ul {
  padding-left: 20px;
  font-size: 14px;
  color: var(--ink-primary);
  line-height: 1.8;
}

.compare-conclusion li {
  margin-bottom: 4px;
}

/* ===== 提示提示 ===== */
.tip-box {
  background: #FFFBEB;
  border: 1px solid #FDE68A;
  border-radius: var(--radius-sm);
  padding: 10px 14px;
  font-size: 13px;
  color: #92400E;
  display: flex;
  align-items: flex-start;
  gap: 8px;
  line-height: 1.6;
}

.tip-box .tip-icon {
  font-size: 16px;
  flex-shrink: 0;
}

/* ===== 颜色选择 ===== */
.color-picker {
  display: flex;
  gap: 6px;
  margin-top: 8px;
}

.color-option {
  width: 22px;
  height: 22px;
  border-radius: 50%;
  cursor: pointer;
  border: 2px solid transparent;
  transition: all 0.2s;
}

.color-option:hover {
  transform: scale(1.1);
}

.color-option.selected {
  border-color: var(--ink-primary);
  transform: scale(1.15);
}

/* ===== 分隔 ===== */
.divider {
  height: 1px;
  background: var(--paper-lines);
  margin: 10px 0;
}

/* ===== 函数对比卡片 ===== */
.compare-func-editor {
  background: var(--paper-bg);
  border-radius: var(--radius-md);
  padding: 12px;
  margin-bottom: 10px;
  border: 1px solid var(--paper-lines);
}

.compare-func-editor .func-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 8px;
}

.compare-func-editor .func-name {
  font-weight: 600;
  font-size: 13px;
  display: flex;
  align-items: center;
  gap: 6px;
}

/* ===== 描点动画 ===== */
.point-animation {
  animation: pointPop 0.4s cubic-bezier(0.34, 1.56, 0.64, 1);
}

@keyframes pointPop {
  0% { transform: scale(0); }
  100% { transform: scale(1); }
}

/* ===== 响应式 ===== */
@media (max-width: 1024px) {
  .app-main {
    grid-template-columns: 1fr;
  }

  .control-panel {
    position: static;
  }

  .properties-grid {
    grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
  }
}

@media (max-width: 640px) {
  .app-header {
    padding: 16px 20px;
  }

  .app-header h1 {
    font-size: 20px;
  }

  .tab-nav {
    padding: 0 16px;
    overflow-x: auto;
  }

  .tab-item {
    padding: 12px 16px;
    font-size: 14px;
    flex-shrink: 0;
  }

  .app-main {
    padding: 16px;
  }

  .chart-container {
    height: 320px;
  }

  .step-nav {
    overflow-x: auto;
  }

  .step-btn {
    flex-shrink: 0;
  }
}

/* 滚动条样式 */
::-webkit-scrollbar {
  width: 8px;
  height: 8px;
}

::-webkit-scrollbar-track {
  background: var(--paper-bg);
  border-radius: 4px;
}

::-webkit-scrollbar-thumb {
  background: var(--paper-grid);
  border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
  background: var(--ink-light);
}