/* ============================================================
   MulticaBoard 教学白板 · 落地页样式
   设计语言：坐标纸（纸白 + 淡蓝格线）× 白板笔墨（墨蓝/朱红/板绿）
   字符系统：系统中文无衬线（正文/标题）· 衬线斜体（方程）· 等宽（眉标）
   ============================================================ */

:root {
  /* 色板 */
  --paper: #f7f9fb;          /* 纸面 */
  --paper-2: #ffffff;        /* 卡片面 */
  --paper-3: #eef2f6;        /* 卡片次级面 */
  --ink: #1b2a3a;            /* 正文墨色 */
  --ink-2: #46586b;          /* 次级文字 */
  --ink-3: #76889a;          /* 弱文字 */
  --line: #d9e1ea;           /* 发丝线 */
  --blue: #2456a6;           /* 白板蓝（主色） */
  --blue-deep: #1a3f7c;
  --blue-soft: #e7edf7;
  --red: #d6493e;            /* 红批注笔 */
  --green: #2f7d5b;          /* 绿白板笔 */
  --board: #14332b;          /* 黑板绿 */
  --board-2: #0f2620;
  --chalk: #efead9;          /* 粉笔白 */

  /* 字体 */
  --sans: "PingFang SC", "Hiragino Sans GB", "Source Han Sans SC",
          "Noto Sans SC", "Microsoft YaHei", system-ui, -apple-system, sans-serif;
  --math: "STIX Two Math", "Latin Modern Math", "Cambria Math",
          Georgia, "Times New Roman", serif;
  --mono: ui-monospace, "SF Mono", "Cascadia Code", Menlo, Consolas,
          "PingFang SC", monospace;

  /* 版式 */
  --wrap: 1120px;
  --radius: 16px;
  --shadow-card: 0 1px 2px rgba(27, 42, 58, 0.05), 0 12px 32px -12px rgba(27, 42, 58, 0.18);
}

/* ---------- 基础 ---------- */

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  font-family: var(--sans);
  font-size: 16px;
  line-height: 1.8;
  color: var(--ink);
  background-color: var(--paper);
  /* 坐标纸底纹：细格 26px + 粗格 130px */
  background-image:
    linear-gradient(to right, rgba(36, 86, 166, 0.055) 1px, transparent 1px),
    linear-gradient(to bottom, rgba(36, 86, 166, 0.055) 1px, transparent 1px),
    linear-gradient(to right, rgba(36, 86, 166, 0.09) 1px, transparent 1px),
    linear-gradient(to bottom, rgba(36, 86, 166, 0.09) 1px, transparent 1px);
  background-size: 26px 26px, 26px 26px, 130px 130px, 130px 130px;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

h1, h2, h3 { line-height: 1.25; margin: 0; }
p { margin: 0; }
a { color: inherit; }

img { max-width: 100%; display: block; }

:focus-visible {
  outline: 2px solid var(--blue);
  outline-offset: 3px;
  border-radius: 4px;
}

.skip-link {
  position: absolute;
  left: -9999px;
  top: 12px;
  z-index: 100;
  background: var(--blue);
  color: #fff;
  padding: 8px 16px;
  border-radius: 8px;
}
.skip-link:focus { left: 12px; }

/* ---------- 按钮 ---------- */

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  padding: 13px 28px;
  border-radius: 10px;
  font-family: var(--sans);
  font-size: 1rem;
  font-weight: 600;
  text-decoration: none;
  border: 1px solid transparent;
  cursor: pointer;
  transition: transform 0.15s ease, box-shadow 0.15s ease, background-color 0.15s ease;
}
.btn:active { transform: translateY(1px); }

.btn-primary {
  background: var(--blue);
  color: #fff;
  box-shadow: 0 10px 24px -10px rgba(36, 86, 166, 0.55);
}
.btn-primary:hover { background: var(--blue-deep); }

.btn-ghost {
  background: transparent;
  color: var(--ink);
  border-color: var(--line);
}
.btn-ghost:hover { border-color: var(--blue); color: var(--blue); }

.btn-chalk {
  background: var(--chalk);
  color: var(--board);
  box-shadow: 0 10px 24px -10px rgba(0, 0, 0, 0.45);
}
.btn-chalk:hover { background: #fff; }

.btn-sm { padding: 9px 20px; font-size: 0.92rem; }

/* ---------- 导航 ---------- */

.nav {
  position: sticky;
  top: 0;
  z-index: 50;
  background: rgba(247, 249, 251, 0.88);
  backdrop-filter: blur(10px);
  -webkit-backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--line);
}

.nav-inner {
  max-width: var(--wrap);
  margin: 0 auto;
  padding: 14px 24px;
  display: flex;
  align-items: center;
  gap: 32px;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  text-decoration: none;
}
.brand-glyph { width: 30px; height: 30px; flex: none; }
.brand-name { font-weight: 700; letter-spacing: -0.01em; }
.brand-sub {
  font-size: 0.8rem;
  color: var(--ink-3);
  border-left: 1px solid var(--line);
  padding-left: 10px;
}

.nav-links {
  display: flex;
  gap: 26px;
  margin-left: auto;
}
.nav-links a {
  font-size: 0.95rem;
  color: var(--ink-2);
  text-decoration: none;
  transition: color 0.15s ease;
}
.nav-links a:hover { color: var(--blue); }

/* ---------- Hero ---------- */

.hero { overflow: hidden; }

.hero-inner {
  max-width: var(--wrap);
  margin: 0 auto;
  padding: 72px 24px 88px;
  display: grid;
  grid-template-columns: 1.05fr 1fr;
  gap: 56px;
  align-items: center;
}

.eyebrow {
  font-family: var(--mono);
  font-size: 0.8rem;
  letter-spacing: 0.12em;
  color: var(--ink-2);
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 22px;
}
.eyebrow-tick {
  display: inline-flex;
  width: 26px;
  height: 26px;
  align-items: center;
  justify-content: center;
  border-radius: 7px;
  background: var(--blue);
  color: var(--chalk);
  font-family: var(--math);
  font-style: italic;
  font-size: 1rem;
  letter-spacing: 0;
}

.hero h1 {
  font-size: clamp(2.5rem, 5.4vw, 4rem);
  font-weight: 700;
  letter-spacing: 0.005em;
  line-height: 1.18;
}

/* 「图形」二字下的手绘正弦下划线 */
.hero-mark { position: relative; display: inline-block; }
.underline-swoosh {
  position: absolute;
  left: 2%;
  bottom: -0.08em;
  width: 96%;
  height: 0.16em;
  overflow: visible;
}
.underline-swoosh path {
  fill: none;
  stroke: var(--red);
  stroke-width: 4;
  stroke-linecap: round;
}

.hero-sub {
  margin-top: 26px;
  font-size: 1.08rem;
  color: var(--ink-2);
  max-width: 34em;
}

.eq-inline {
  font-family: var(--math);
  font-style: italic;
  color: var(--blue);
  white-space: nowrap;
}

.hero-actions {
  margin-top: 36px;
  display: flex;
  flex-wrap: wrap;
  gap: 14px;
}

.hero-note {
  margin-top: 18px;
  font-size: 0.85rem;
  color: var(--ink-3);
  letter-spacing: 0.02em;
}

/* ---------- 白板演示卡（签名元素） ---------- */

.hero-demo { min-width: 0; }

.board-card {
  background: var(--paper-2);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow-card);
  overflow: hidden;
}

.board-toolbar {
  display: flex;
  align-items: center;
  gap: 6px;
  padding: 9px 14px;
  border-bottom: 1px solid var(--line);
  background: var(--paper-3);
}

.tool {
  width: 30px;
  height: 30px;
  border-radius: 8px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  color: var(--ink-3);
  font-size: 0.85rem;
  font-weight: 600;
  background: transparent;
}
.tool-fn { font-family: var(--math); font-style: italic; font-size: 1.05rem; }
.tool.is-active {
  background: var(--blue);
  color: var(--chalk);
}

/* 工具条里的极简图标（纯 CSS 绘制，避免装饰性 SVG 堆砌） */
.tool-pen::before { content: "✎"; font-size: 0.95rem; }
.tool-rect::before {
  content: "";
  width: 12px;
  height: 9px;
  border: 1.6px solid currentColor;
  border-radius: 2px;
}
.tool-circle::before {
  content: "";
  width: 11px;
  height: 11px;
  border: 1.6px solid currentColor;
  border-radius: 50%;
}

.toolbar-tail {
  margin-left: auto;
  font-size: 0.75rem;
  color: var(--ink-3);
  font-family: var(--mono);
  letter-spacing: 0.05em;
}

.board-plot { padding: 6px 10px 0; }
.board-plot svg { display: block; width: 100%; height: auto; }
.board-plot-tall svg { max-height: 430px; }

.board-input {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 13px 16px;
  border-top: 1px solid var(--line);
  background: var(--paper-3);
  font-size: 1.05rem;
  flex-wrap: wrap;
}
.board-input-multi { gap: 8px 18px; }

.fn-badge {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 26px;
  height: 26px;
  border-radius: 7px;
  background: var(--blue);
  color: var(--chalk);
  font-family: var(--math);
  font-style: italic;
  font-size: 1rem;
  flex: none;
}
.fn-badge-2 { background: var(--red); }
.fn-badge-3 { background: var(--green); }

.eq { font-family: var(--math); }
.eq i { font-style: italic; }

.caret {
  width: 2px;
  height: 1.25em;
  background: var(--blue);
  animation: blink 1s steps(1) infinite;
}
@keyframes blink { 50% { opacity: 0; } }

/* 方程切换 chips */
.chips {
  margin-top: 16px;
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  justify-content: center;
}

.chip {
  font-family: var(--math);
  font-size: 0.95rem;
  padding: 8px 16px;
  border-radius: 999px;
  border: 1px solid var(--line);
  background: var(--paper-2);
  color: var(--ink-2);
  cursor: pointer;
  transition: border-color 0.15s ease, color 0.15s ease, box-shadow 0.15s ease;
}
.chip:hover { border-color: var(--blue); color: var(--blue); }
.chip.is-active {
  border-color: var(--blue);
  color: var(--blue);
  background: var(--blue-soft);
  box-shadow: inset 0 0 0 1px var(--blue);
}

/* ---------- 通用小节 ---------- */

.section {
  max-width: var(--wrap);
  margin: 0 auto;
  padding: 84px 24px 30px;
  scroll-margin-top: 72px;
}

.section-head { max-width: 620px; margin-bottom: 46px; }

.section-eyebrow {
  display: flex;
  align-items: center;
  gap: 12px;
  font-family: var(--mono);
  font-size: 0.8rem;
  letter-spacing: 0.12em;
  color: var(--ink-2);
  margin-bottom: 16px;
}
.sec-no {
  color: var(--red);
  border: 1px solid currentColor;
  border-radius: 6px;
  padding: 1px 7px;
  font-size: 0.72rem;
}

.section h2 {
  font-size: clamp(1.7rem, 3.2vw, 2.35rem);
  font-weight: 700;
  letter-spacing: 0.005em;
}

.section-sub { margin-top: 18px; color: var(--ink-2); }

/* ---------- §1 出图 showcase ---------- */

.showcase {
  display: grid;
  grid-template-columns: 1.6fr 1fr;
  gap: 28px;
  align-items: stretch;
}

.props {
  background: var(--paper-2);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow-card);
  padding: 24px 26px;
  display: flex;
  flex-direction: column;
}

.props-title {
  font-family: var(--mono);
  font-size: 0.78rem;
  letter-spacing: 0.1em;
  color: var(--ink-3);
  margin-bottom: 18px;
}

.prop {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 12px;
  padding: 11px 0;
  border-bottom: 1px dashed var(--line);
}
.prop-label { color: var(--ink-2); font-size: 0.95rem; }
.prop-value {
  font-family: var(--mono);
  font-size: 0.88rem;
  color: var(--ink);
  display: inline-flex;
  align-items: center;
  gap: 8px;
}

.dot-check {
  width: 16px;
  height: 16px;
  border-radius: 5px;
  background: var(--blue);
  position: relative;
  display: inline-block;
}
.dot-check::after {
  content: "";
  position: absolute;
  left: 5px;
  top: 2.5px;
  width: 4px;
  height: 8px;
  border: solid #fff;
  border-width: 0 2px 2px 0;
  transform: rotate(42deg);
}

.swatch {
  width: 15px;
  height: 15px;
  border-radius: 50%;
  display: inline-block;
  border: 1px solid rgba(0, 0, 0, 0.12);
}
.swatch-blue { background: var(--blue); }
.swatch-red { background: var(--red); }
.swatch-green { background: var(--green); }

.families {
  list-style: none;
  margin: 18px 0 0;
  padding: 0;
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}
.families li {
  font-size: 0.82rem;
  color: var(--ink-2);
  background: var(--blue-soft);
  border-radius: 999px;
  padding: 4px 13px;
}

.props-note {
  margin-top: auto;
  padding-top: 18px;
  font-size: 0.85rem;
  color: var(--ink-3);
}

/* ---------- §2 功能网格 ---------- */

.feature-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 20px;
}

.feature {
  background: var(--paper-2);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 26px 26px 24px;
  transition: transform 0.2s ease, box-shadow 0.2s ease, border-color 0.2s ease;
}
.feature:hover {
  transform: translateY(-3px);
  box-shadow: var(--shadow-card);
  border-color: #c6d3e2;
}

.feature-icon {
  display: inline-flex;
  width: 44px;
  height: 44px;
  align-items: center;
  justify-content: center;
  border-radius: 12px;
  background: var(--blue-soft);
  color: var(--blue);
  margin-bottom: 16px;
}
.feature-icon svg { width: 22px; height: 22px; }

.feature h3 { font-size: 1.06rem; font-weight: 650; }
.feature p { margin-top: 8px; font-size: 0.92rem; color: var(--ink-2); line-height: 1.75; }

/* ---------- §3 场景 ---------- */

.scene-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 20px;
}

.scene {
  border-top: 3px solid var(--blue);
  background: var(--paper-2);
  border-radius: 0 0 var(--radius) var(--radius);
  padding: 26px;
  box-shadow: var(--shadow-card);
}
.scene:nth-child(2) { border-top-color: var(--red); }
.scene:nth-child(3) { border-top-color: var(--green); }

.scene-when {
  font-family: var(--mono);
  font-size: 0.78rem;
  letter-spacing: 0.14em;
  color: var(--ink-3);
  margin-bottom: 14px;
}
.scene h3 { font-size: 1.12rem; }
.scene p { margin-top: 12px; font-size: 0.94rem; color: var(--ink-2); }

/* ---------- §4 实拍 ---------- */

.gallery {
  display: grid;
  grid-template-columns: 1fr;
  gap: 28px;
}

.shot {
  margin: 0;
  background: var(--paper-2);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow-card);
  overflow: hidden;
}
.shot img { width: 100%; height: auto; border-bottom: 1px solid var(--line); }
.shot figcaption {
  padding: 14px 20px;
  font-size: 0.9rem;
  color: var(--ink-2);
}

/* ---------- 黑板 CTA ---------- */

.cta-board {
  margin-top: 90px;
  background: linear-gradient(180deg, var(--board) 0%, var(--board-2) 100%);
  color: var(--chalk);
  position: relative;
  overflow: hidden;
}

.cta-inner {
  max-width: var(--wrap);
  margin: 0 auto;
  padding: 96px 24px 40px;
  text-align: center;
  position: relative;
  z-index: 1;
}

.cta-eyebrow {
  font-family: var(--mono);
  font-size: 0.82rem;
  letter-spacing: 0.3em;
  color: rgba(239, 234, 217, 0.65);
  margin-bottom: 18px;
}

.cta-board h2 {
  font-size: clamp(2rem, 4.4vw, 3.1rem);
  font-weight: 700;
}

.cta-sub {
  margin-top: 16px;
  color: rgba(239, 234, 217, 0.78);
  font-size: 1.05rem;
}

.cta-board .btn { margin-top: 36px; }

.cta-curve {
  display: block;
  width: 100%;
  height: 130px;
  margin-top: 30px;
}
.cta-curve path {
  fill: none;
  stroke: rgba(239, 234, 217, 0.34);
  stroke-width: 2.5;
  stroke-dasharray: 2 9;
  stroke-linecap: round;
}

/* ---------- 页脚 ---------- */

.footer {
  background: var(--board-2);
  color: rgba(239, 234, 217, 0.8);
  border-top: 1px solid rgba(239, 234, 217, 0.14);
}

.footer-inner {
  max-width: var(--wrap);
  margin: 0 auto;
  padding: 34px 24px;
  display: flex;
  align-items: center;
  gap: 28px;
  flex-wrap: wrap;
}

.brand-footer .brand-name { color: var(--chalk); }

.footer-links {
  display: flex;
  gap: 22px;
  margin-left: auto;
  flex-wrap: wrap;
}
.footer-links a {
  color: rgba(239, 234, 217, 0.72);
  text-decoration: none;
  font-size: 0.92rem;
}
.footer-links a:hover { color: var(--chalk); }

.footer-copy {
  font-size: 0.82rem;
  color: rgba(239, 234, 217, 0.45);
  width: 100%;
  margin: 0;
}

/* ---------- 进场动效 ---------- */

.reveal {
  opacity: 0;
  transform: translateY(16px);
  transition: opacity 0.65s ease, transform 0.65s ease;
}
.reveal.in { opacity: 1; transform: none; }

.feature-grid .reveal:nth-child(2),
.scene-grid .reveal:nth-child(2) { transition-delay: 0.08s; }
.feature-grid .reveal:nth-child(3),
.scene-grid .reveal:nth-child(3) { transition-delay: 0.16s; }
.feature-grid .reveal:nth-child(5) { transition-delay: 0.08s; }
.feature-grid .reveal:nth-child(6) { transition-delay: 0.16s; }

/* ---------- SVG 出图内部样式（由 js 注入内容） ---------- */

.plot-grid-minor { stroke: rgba(36, 86, 166, 0.1); stroke-width: 1; }
.plot-grid-major { stroke: rgba(36, 86, 166, 0.18); stroke-width: 1; }
.plot-axis { stroke: var(--ink-2); stroke-width: 1.5; }
.plot-tick-label {
  font-family: var(--mono);
  font-size: 11px;
  fill: var(--ink-3);
}
.plot-curve {
  fill: none;
  stroke-width: 3;
  stroke-linecap: round;
  stroke-linejoin: round;
}
.plot-curve-blue { stroke: var(--blue); }
.plot-curve-red { stroke: var(--red); }
.plot-curve-green { stroke: var(--green); }
.plot-label {
  font-family: var(--math);
  font-size: 15px;
  fill: var(--ink-2);
}

/* ---------- 响应式 ---------- */

@media (max-width: 980px) {
  .hero-inner {
    grid-template-columns: 1fr;
    padding-top: 56px;
    padding-bottom: 64px;
    gap: 44px;
  }
  .showcase { grid-template-columns: 1fr; }
  .feature-grid, .scene-grid { grid-template-columns: repeat(2, 1fr); }
}

@media (max-width: 640px) {
  .nav-inner { gap: 14px; padding: 12px 18px; }
  .nav-links { display: none; }
  .nav .btn { margin-left: auto; }
  .brand-sub { display: none; }
  .section { padding: 64px 18px 22px; }
  .feature-grid, .scene-grid { grid-template-columns: 1fr; }
  .hero-actions .btn { flex: 1 1 auto; }
  .toolbar-tail { display: none; }
  .cta-inner { padding-top: 72px; }
}

/* ---------- 动效克制 ---------- */

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  .reveal {
    opacity: 1;
    transform: none;
    transition: none;
  }
  .caret { animation: none; }
  .feature:hover { transform: none; }
  * {
    transition-duration: 0.01ms !important;
    animation-duration: 0.01ms !important;
  }
}