/* ============================================================
   intro.css — 问题引入：兔子繁衍 × 杨辉三角 × 数学家 accordion
   （斐波那契教学页面 · 样式封装 part 3）
   注意：图片相对路径指向 ../image/
   ============================================================ */

#intro { scroll-margin-top: 80px; }

/* ---- 左右两栏（兔子 + 杨辉三角） ---- */
.intro-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 26px;
  margin-bottom: 60px;
}
@media (max-width: 900px) { .intro-grid { grid-template-columns: 1fr; } }
.intro-card {
  background: var(--card);
  border: 1px solid var(--card-border);
  border-radius: var(--radius);
  padding: 26px;
  backdrop-filter: blur(6px);
  box-shadow: var(--shadow);
  display: flex;
  flex-direction: column;
  overflow: hidden;   /* 兜底：任何子内容溢出都裁剪在卡片内，避免右侧露出/撑破 */
}

/* 兔子 / 垛积术：把交互卡片做成"图挂"背景（图片偏亮 → 叠加深色玻璃遮罩保证文字清晰） */
.intro-card--rabbit {
  position: relative;
  background-image:
    linear-gradient(180deg, rgba(15,21,36,0.82), rgba(15,21,36,0.9)),
    url('../image/兔子图片.jpg');
  background-size: cover;
  background-position: center center;
  border-color: rgba(251,191,36,0.25);
}
.intro-card--triangle {
  position: relative;
  background-image:
    linear-gradient(180deg, rgba(15,21,36,0.82), rgba(15,21,36,0.9)),
    url('../image/垛积术图片.jpg');
  background-size: cover;
  background-position: center center;
  border-color: rgba(45,212,191,0.25);
}
/* 鼠标悬停时略微压暗遮罩、透出更多图片，提示可交互 */
.intro-card--rabbit:hover { background-image: linear-gradient(180deg, rgba(15,21,36,0.7), rgba(15,21,36,0.82)), url('../image/兔子图片.jpg'); }
.intro-card--triangle:hover { background-image: linear-gradient(180deg, rgba(15,21,36,0.7), rgba(15,21,36,0.82)), url('../image/垛积术图片.jpg'); }

/* 卡片底部"图源"角标 */
.intro-card--rabbit::after,
.intro-card--triangle::after {
  content: attr(data-badge);
  position: absolute;
  right: 14px; bottom: 12px;
  font-size: 0.72rem; letter-spacing: 1px;
  color: var(--text);
  background: rgba(15,21,36,0.65);
  border: 1px solid var(--card-border);
  padding: 4px 12px; border-radius: 20px;
}
.intro-card--rabbit::after { color: var(--gold-1); }
.intro-card--triangle::after { color: var(--teal); }

/* ---- 兔子繁衍交互 ---- */
.rabbit-stage { margin-top: 6px; }
.rabbit-field {
  position: relative;
  min-height: 132px;
  background: rgba(255,255,255,0.02);
  border: 1px dashed var(--card-border);
  border-radius: 14px;
  padding: 12px;
  display: flex;
  align-items: flex-start;
  justify-content: center;
  overflow-y: auto;
}
.rabbit-track {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: center;
  gap: 4px;
  max-width: 100%;
}
.rabbit-pair {
  width: 32px; height: 32px;
  border-radius: 50%;
  font-size: 1.25rem;
  line-height: 1;
  display: grid; place-items: center;
  flex-shrink: 0;
  background: radial-gradient(circle at 35% 30%, #fde68a, #f59e0b);
  animation: popIn 0.4s ease both;
}
.rabbit-pair.adult { background: radial-gradient(circle at 35% 30%, #f9a8d4, #db2777); }
.rabbit-meta {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin: 12px 2px 6px;
  font-size: 0.95rem;
  color: var(--muted);
}
.rabbit-month { color: var(--gold-1); font-weight: 800; }
.rabbit-count { color: var(--text); font-weight: 700; }
.rabbit-stage input[type=range] { width: 100%; accent-color: var(--gold-1); }
.rabbit-sequence {
  margin-top: 10px;
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  justify-content: center;
}
.rabbit-seq-chip {
  min-width: 34px; height: 34px;
  display: grid; place-items: center;
  border-radius: 8px;
  background: var(--card);
  border: 1px solid var(--card-border);
  font-weight: 800;
  font-size: 0.85rem;
  color: var(--muted);
}
.rabbit-seq-chip.active {
  background: linear-gradient(135deg, var(--gold-1), var(--gold-2));
  color: #0f1524;
  border-color: transparent;
  box-shadow: 0 4px 12px rgba(251,191,36,0.35);
}

/* ---- 杨辉三角 ---- */
.yanghui-wrap {
  margin-top: 4px;
  padding: 16px;
  background: rgba(15,21,36,0.06);
  border: 1px solid var(--card-border);
  border-radius: var(--radius);
}
.yanghui-tri {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 6px;
  overflow-x: auto;
}
.yh-row { display: flex; gap: 6px; justify-content: center; }
.yh-cell {
  min-width: 40px;
  height: 40px;
  display: grid; place-items: center;
  padding: 0 10px;
  background: rgba(255,255,255,0.06);
  border: 1px solid var(--card-border);
  border-radius: 8px;
  font-weight: 700;
  font-size: 0.95rem;
  color: var(--text);
  cursor: pointer;
  /* 只过渡颜色，避免 shadow/transform 渐变在行间缝隙反复切换时产生闪烁抽搐 */
  transition: background-color 0.15s ease, border-color 0.15s ease, color 0.15s ease;
  animation: fadeSlide 0.4s ease both;
  backdrop-filter: blur(3px);
  will-change: auto;
}
.yh-cell:hover {
  /* 用背景/边框反馈代替位移，避免行间 hover 引发的布局抖动 */
  transform: none;
  background: rgba(255,255,255,0.14);
  border-color: rgba(251,191,36,0.6);
}
.yh-cell.fib {
  background: linear-gradient(135deg, var(--gold-1), var(--gold-2));
  color: #0f1524;
  border-color: transparent;
  box-shadow: 0 2px 8px rgba(251,191,36,0.35);
  font-weight: 800;
  transform: none;
}
.yh-cell.fib:hover { transform: none; }
.yanghui-note {
  margin-top: 14px;
  padding-top: 12px;
  border-top: 1px solid var(--card-border);
  text-align: center;
  font-size: 1rem;
  color: var(--text);
  /* 固定最小高度，避免悬停时文案高度变化引起卡片布局抖动/抽搐 */
  min-height: 96px;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  gap: 6px;
}
.yanghui-note .fib-nums {
  display: inline-block;
  margin-top: 6px;
  color: var(--gold-1);
  font-weight: 800;
  letter-spacing: 3px;
  font-size: 1.1rem;
}

/* ---- 数学家横向折叠 accordion ---- */
.mat-section { margin-top: 10px; }
.mat-accordion {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 18px;
  align-items: start;
}
.mat-item {
  background: var(--card);
  border: 1px solid var(--card-border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  overflow: hidden;
    opacity: 0;
  transform: translateX(-70px);
  transition:
    transform 0.5s cubic-bezier(0.2, 0.8, 0.2, 1),
    opacity 0.5s ease,
    border-color 0.3s;
}
.mat-item.entered { opacity: 1; transform: translateX(0); }
.mat-item:hover { border-color: var(--gold-1); }
.mat-head {
  width: 100%;
  background: transparent;
  border: none;
  cursor: pointer;
  padding: 16px 18px;
  display: flex;
  align-items: center;
  gap: 14px;
  color: var(--text);
  font-family: inherit;
  text-align: left;
}
.mat-title { flex: 1; }
.mat-title strong { display: block; font-size: 1.02rem; }
.mat-title small { color: var(--muted); font-size: 0.78rem; }
.mat-chev {
  font-size: 1.5rem;
  color: var(--gold-1);
  line-height: 1;
  transition: transform 0.35s;
  flex-shrink: 0;
}
.mat-item.open .mat-chev { transform: rotate(90deg); }
.mat-body {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.5s ease;
  padding: 0 20px;
}
.mat-item.open .mat-body { max-height: 900px; }
.mat-body .mat-bio,
.mat-link { color: var(--text); font-size: 0.92rem; line-height: 1.7; }
.mat-body .mat-bio { padding-bottom: 10px; }
.mat-facts { padding: 0 0 4px 18px; margin: 0 0 10px; color: var(--muted); font-size: 0.88rem; }
.mat-facts li { margin-bottom: 6px; }
.mat-link {
  background: rgba(251,191,36,0.06);
  border-left: 3px solid var(--gold-1);
  padding: 10px 14px;
  border-radius: 0 8px 8px 0;
  margin-bottom: 14px;
}
.mat-link .fib-str { color: var(--gold-1); font-weight: 800; letter-spacing: 1px; }
.mat-quote {
  font-style: italic;
  color: var(--muted);
  border-left: 3px solid var(--teal);
  padding: 6px 14px;
  font-size: 0.85rem;
  margin: 0 0 18px;
}
.mat-avatar {
  width: 70px; height: 70px;
  border-radius: 50%;
  display: grid; place-items: center;
  font-size: 2rem;
  position: relative;
  overflow: hidden;
  flex-shrink: 0;
}
.mat-avatar em {
  position: absolute;
  right: 5px; bottom: 2px;
  font-style: normal;
  font-size: 1rem;
  font-weight: 800;
  color: #0f1524;
}
.av-fib { background: radial-gradient(circle at 30% 30%, #fde68a, #f59e0b); box-shadow: 0 6px 20px rgba(251,191,36,0.4); }
.av-jiaxian { background: radial-gradient(circle at 30% 30%, #99f6e4, #0d9488); box-shadow: 0 6px 20px rgba(45,212,191,0.4); }
.av-yanghui { background: radial-gradient(circle at 30% 30%, #ddd6fe, #7c3aed); box-shadow: 0 6px 20px rgba(167,139,250,0.4); }

/* 宽屏（≥1100px）：点击展开时，将展开的卡片横向扩张 */
.mat-item.expand {
  grid-column: span 1;
  transform: scale(1.02);
  border-color: var(--gold-1);
}
@media (max-width: 900px) {
  .mat-accordion { grid-template-columns: 1fr; }
}

/* ============================================================
   问题引入页 · 分方向入场动画
   （覆盖 base.css 中 .reveal 的统一 3D 翻转：
     上方标题从上方滑入、左兔子卡片从左侧滑入、
     右垛积术卡片从右侧滑入、数学家区域保持从左侧弹出）
   ============================================================ */
/* 上方标题：3D 飞入（从空间上方高处、略带俯仰地飞入正面） */
#intro .sec-head.reveal {
  transform:
    perspective(1200px)
    rotateX(26deg)
    translateY(-80px)
    translateZ(-180px)
    scale(0.72);
  transform-origin: 50% 0%;
}
/* 左兔子卡：从左侧滑入 */
#intro .reveal-left.reveal {
  transform: translateX(-130px);
}
/* 右垛积术卡：从右侧滑入 */
#intro .reveal-right.reveal {
  transform: translateX(130px);
}
/* 数学家区域：整体从左侧横向滑入 */
#intro .mat-section.reveal {
  transform: translateX(-120px);
}
/* 数学家卡片在容器内不各自错落弹出，随大块一起同步滑入 */
#intro .mat-item {
  transition-delay: 0s !important;
}
/* 归位 */
#intro .sec-head.reveal.visible {
  transform: perspective(1200px) rotateX(0deg) translateY(0) translateZ(0) scale(1);
  transform-origin: 50% 50%;
}
#intro .reveal-left.reveal.visible,
#intro .reveal-right.reveal.visible,
#intro .mat-section.reveal.visible {
  transform: translateX(0);
}

/* ============================================================
   手机端适配：收窄卡片内边距、缩小杨辉三角格子，
   让兔子数列与杨辉三角完整放下、不再被裁掉右侧
   ============================================================ */
@media (max-width: 520px) {
  .intro-card { padding: 18px 14px; }
  .rabbit-field { padding: 10px; overflow-x: hidden; }
  .rabbit-track { width: 100%; }
  .yanghui-wrap { padding: 10px; }
  .yanghui-tri { gap: 4px; }
  .yh-row { gap: 4px; }
  .yh-cell {
    min-width: 26px; height: 34px;
    padding: 0 5px;
    font-size: 0.82rem;
    flex: 0 1 auto;
  }
}