:root {
  color-scheme: light;
  --paper: #fbfcff;
  --white: #fff;
  --ink: #121825;
  --blue: #254ed8;
  --blue-dark: #1b3ca8;
  --muted: #536078;
  --line: #dee4ef;
  --soft: #f0f3fb;
  --radius: 22px;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Noto Sans", "PingFang SC", "Microsoft YaHei", sans-serif;
  font-synthesis: none;
  text-rendering: optimizeLegibility;
}
* { box-sizing: border-box; }
html { scroll-behavior: smooth; scroll-padding-top: 105px; }
body { margin: 0; background: var(--paper); color: var(--ink); }
a { color: inherit; text-decoration: none; }
button, input { font: inherit; }
img, svg { display: block; max-width: 100%; }
p, h1, h2, h3 { margin: 0; }
p { line-height: 1.7; }
::selection { background: #dce5ff; color: var(--ink); }
:focus-visible { outline: 3px solid var(--blue); outline-offset: 5px; }
.wrap { width: min(1224px, calc(100% - 96px)); margin-inline: auto; }
.skip-link { position: absolute; top: 12px; left: 20px; z-index: 30; padding: 12px 18px; background: var(--ink); color: white; border-radius: 8px; transform: translateY(-170%); }
.skip-link:focus { transform: translateY(0); }
.site-header { position: sticky; top: 0; z-index: 20; background: rgba(251, 252, 255, .97); border-bottom: 1px solid var(--line); }
.header-inner { min-height: 88px; display: flex; align-items: center; gap: 28px; }
.site-wordmark { display: inline-flex; align-items: baseline; font-size: 35px; line-height: 1; font-weight: 740; letter-spacing: -2px; }
.wordmark-dot { color: var(--blue); }
.wordmark-chinese { margin-left: 15px; font-size: 14px; letter-spacing: .08em; font-weight: 540; }
.header-nav { display: flex; align-items: center; gap: 34px; margin-left: auto; font-size: 13px; font-weight: 550; }
.header-nav a { padding-block: 12px; }
.header-nav a:hover, .footer-nav a:hover, .intro-link:hover { color: var(--blue); }
.language-link { display: inline-flex; align-items: center; gap: 9px; font-size: 13px; padding: 10px 14px; border: 1px solid var(--line); border-radius: 8px; min-height: 44px; }
.language-link:hover { background: var(--soft); }
.hero { display: grid; grid-template-columns: 1.02fr 1fr; align-items: center; gap: 60px; padding-block: 85px 80px; }
.eyebrow { font-size: 11px; letter-spacing: .14em; font-weight: 640; text-transform: uppercase; line-height: 1.6; }
.hero-copy > .eyebrow { display: flex; align-items: center; gap: 10px; color: var(--muted); margin-bottom: 27px; }
.small-line { width: 23px; height: 2px; flex-shrink: 0; background: var(--blue); }
h1 { font-size: clamp(50px, 5.3vw, 74px); line-height: 1.08; letter-spacing: -.055em; font-weight: 650; }
.blue-word { color: var(--blue); }
.hero-description { max-width: 470px; font-size: 17px; color: var(--muted); margin-top: 26px; }
.hero-actions { display: flex; flex-wrap: wrap; align-items: center; gap: 20px 22px; margin-top: 32px; }
.button { display: inline-flex; justify-content: center; align-items: center; gap: 22px; min-height: 52px; padding: 14px 21px; border: 1px solid transparent; border-radius: 9px; font-size: 14px; font-weight: 620; line-height: 1.4; transition: background .16s, border-color .16s, transform .16s; }
.button span { font-size: 18px; line-height: 1; }
.button:hover { transform: translateY(-2px); }
.button-primary { background: var(--blue); color: var(--white); }
.button-primary:hover { background: var(--blue-dark); }
.button-secondary { background: var(--white); border-color: #cbd4e8; color: var(--ink); }
.button-secondary:hover { border-color: var(--blue); background: #f5f7ff; }
.text-link { display: inline-flex; align-items: center; gap: 15px; min-height: 44px; font-size: 13px; font-weight: 550; }
.text-link:hover { color: var(--blue); }
.hero-note { margin-top: 27px; font-size: 11px; color: var(--muted); letter-spacing: .025em; }
.hero-note span { padding-inline: 8px; color: #b3bdcf; }
.explorer { position: relative; padding: 26px 26px 22px; background: var(--soft); border: 1px solid #e2e7f2; border-radius: var(--radius); }
.explorer-heading { display: flex; justify-content: space-between; gap: 16px; align-items: center; }
.explorer-heading .eyebrow { font-size: 10px; color: var(--muted); }
.explorer-heading h2 { font-size: 18px; margin-top: 7px; letter-spacing: -.03em; font-weight: 580; }
.math-token { display: grid; place-items: center; width: 44px; height: 44px; flex-shrink: 0; color: var(--blue); border: 1px solid #d8e0f5; background: var(--white); border-radius: 12px; font: italic 23px Georgia, serif; }
.function-graph { width: 100%; margin-top: 10px; overflow: visible; }
.graph-grid path { stroke: #dfe5f2; fill: none; }
.graph-axes path { stroke: #b0bacd; stroke-width: 1.2; fill: none; }
.graph-labels { fill: #64728b; font-size: 13px; text-anchor: middle; }
.graph-curve { fill: none; stroke: var(--blue); stroke-width: 3; stroke-linecap: round; }
.graph-equation rect { fill: var(--white); }
.graph-equation text { fill: var(--blue); font: italic 19px Georgia, serif; text-anchor: middle; }
.graph-guides { stroke: var(--blue); stroke-width: 1.2; stroke-dasharray: 4 5; opacity: .48; }
.graph-point-halo { fill: var(--blue); opacity: .09; }
.graph-point { fill: var(--blue); stroke: var(--white); stroke-width: 3; }
.explorer-controls { background: var(--white); border-radius: 12px; padding: 16px 19px 12px; }
.explorer-controls label { display: flex; justify-content: space-between; gap: 12px; font-size: 12px; font-weight: 590; align-items: baseline; }
.sample-values { color: var(--blue); font-size: 12px; font-weight: 500; font-variant-numeric: tabular-nums; }
input[type="range"] { display: block; width: 100%; min-height: 40px; accent-color: var(--blue); cursor: pointer; margin: 5px 0 0; }
.explorer-controls p { font-size: 10px; color: var(--muted); }
.explorer-controls .no-script-note { font-size: 11px; margin-top: 8px; }
.intro-line { display: flex; align-items: center; justify-content: space-between; gap: 30px; padding-block: 27px; border-top: 1px solid var(--line); border-bottom: 1px solid var(--line); }
.intro-line p { font-size: 15px; color: var(--muted); line-height: 1.55; }
.intro-line strong { color: var(--ink); font-weight: 550; }
.intro-link { display: flex; align-items: center; gap: 33px; font-size: 12px; }
.intro-link span { font-size: 25px; color: var(--blue); }
.section-space { padding-block: 95px; }
.product-section { display: grid; grid-template-columns: .98fr 1.1fr; gap: 100px; }
.product-identity { display: flex; gap: 15px; align-items: center; margin-bottom: 28px; }
.product-identity img { width: 56px; height: 56px; border-radius: 13px; border: 1px solid #233f42; }
.product-identity .eyebrow { font-size: 10px; color: var(--muted); }
.product-name { font-size: 19px; font-weight: 600; letter-spacing: -.03em; line-height: 1.4; margin-top: 3px; }
h2 { font-size: clamp(32px, 3.3vw, 46px); line-height: 1.17; font-weight: 620; letter-spacing: -.04em; }
.section-description { color: var(--muted); font-size: 15px; max-width: 430px; }
.section-intro .section-description { margin-top: 24px; }
.product-features { display: grid; grid-template-columns: 1fr 1fr; gap: 36px 32px; padding-top: 8px; }
.feature-index { display: block; font-size: 10px; font-variant-numeric: tabular-nums; color: var(--blue); padding-bottom: 13px; border-bottom: 1px solid var(--line); margin-bottom: 16px; }
h3 { font-size: 17px; line-height: 1.4; font-weight: 610; letter-spacing: -.025em; }
.product-features p { font-size: 13px; line-height: 1.75; color: var(--muted); margin-top: 10px; }
.working-section { background: var(--ink); color: var(--white); }
.working-inner { display: grid; grid-template-columns: .9fr 1fr; align-items: center; gap: 110px; padding-block: 72px; }
.working-copy .eyebrow { color: #a8b5ce; margin-bottom: 23px; }
.working-copy h2 { font-size: clamp(42px, 4.5vw, 61px); line-height: 1.11; }
.working-copy h2 span { color: #a8bdff; }
.working-copy > p:last-child { font-size: 14px; line-height: 1.8; color: #b6c1d5; margin-top: 25px; max-width: 380px; }
.working-example { background: #f7f9fe; color: var(--ink); padding: 25px 28px 20px; border-radius: 18px; }
.example-topline { display: flex; gap: 8px; align-items: center; color: var(--muted); font-size: 10px; padding-bottom: 20px; border-bottom: 1px solid var(--line); }
.example-topline > span:last-child { margin-left: auto; color: var(--blue); font-size: 17px; }
.example-dot { width: 6px; height: 6px; border-radius: 50%; background: var(--blue); }
.example-question { margin-top: 25px; font-size: 18px; line-height: 1.5; font-weight: 520; }
.example-equation { display: flex; flex-wrap: wrap; align-items: center; gap: 20px; margin-block: 28px; color: var(--blue); font: italic 27px Georgia, serif; line-height: 1.5; }
.equation-arrow { font: 18px system-ui, sans-serif; color: #8894ac; }
.example-reasoning { display: flex; gap: 14px; align-items: center; padding: 16px; background: #e9eefb; border-radius: 11px; }
.reasoning-mark { font: 27px Georgia, serif; color: var(--blue); }
.example-reasoning p { font-size: 12px; color: #40516f; }
.working-modes { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 24px; }
.working-modes span { display: inline-flex; gap: 7px; align-items: center; border: 1px solid var(--line); border-radius: 6px; padding: 5px 8px; font-size: 9px; color: var(--muted); }
.working-modes b { font-size: 12px; font-weight: 500; color: #263755; }
.section-title-row { display: flex; justify-content: space-between; align-items: end; gap: 50px; }
.section-title-row .eyebrow { color: var(--blue); margin-bottom: 19px; }
.section-title-row .section-description { max-width: 390px; padding-bottom: 2px; }
.learning-steps { list-style: none; padding: 0; margin: 44px 0 0; display: grid; grid-template-columns: repeat(3, 1fr); gap: 42px; }
.learning-steps li { border-top: 1px solid var(--line); padding-top: 22px; }
.step-number { display: block; font-size: 12px; color: var(--blue); margin-bottom: 30px; }
.learning-steps h3 { font-size: 20px; }
.learning-steps p { color: var(--muted); font-size: 14px; margin-top: 14px; }
.step-footnote { display: block; font-size: 10px; letter-spacing: .015em; color: #64718a; margin-top: 27px; }
.start-section { border-top: 1px solid var(--line); padding-top: 72px; padding-bottom: 62px; }
.entry-options { display: grid; grid-template-columns: 1fr 1fr; gap: 24px; margin-top: 36px; }
.entry-option { position: relative; padding: 35px; border-radius: 18px; border: 1px solid #dce3f1; background: var(--soft); }
.entry-app { background: var(--white); }
.entry-symbol { display: block; font-size: 30px; font-weight: 300; color: var(--blue); margin-bottom: 30px; }
.entry-option .eyebrow { color: var(--muted); font-size: 10px; margin-bottom: 12px; }
.entry-option h3 { font-size: 25px; }
.entry-option > p:not(.eyebrow):not(.entry-detail) { margin-top: 15px; color: var(--muted); max-width: 360px; font-size: 14px; min-height: 71px; }
.entry-option .button { margin-top: 25px; }
.entry-option .entry-detail { font-size: 11px; line-height: 1.6; color: #64718a; margin-top: 16px; max-width: 370px; }
.questions-section { display: grid; grid-template-columns: .65fr 1.2fr; gap: 95px; padding-block: 15px 70px; }
.questions-section > h2 { font-size: 25px; padding-top: 19px; }
.questions-list details { border-bottom: 1px solid var(--line); }
.questions-list details:first-child { border-top: 1px solid var(--line); }
.questions-list summary { display: flex; align-items: center; gap: 16px; justify-content: space-between; cursor: pointer; list-style: none; font-size: 14px; line-height: 1.5; font-weight: 560; padding-block: 20px; }
.questions-list summary::-webkit-details-marker { display: none; }
.questions-list summary > span { color: var(--blue); font-size: 22px; line-height: 1; flex-shrink: 0; transition: transform .15s; }
.questions-list details[open] summary > span { transform: rotate(45deg); }
.questions-list details p { color: var(--muted); font-size: 13px; padding-bottom: 20px; padding-right: 30px; }
.questions-list details a { color: var(--blue); text-decoration: underline; text-underline-offset: 3px; }
.closing-section { display: flex; align-items: center; justify-content: space-between; gap: 40px; border-top: 1px solid var(--line); padding-block: 55px 65px; }
.closing-section .eyebrow { margin-bottom: 15px; color: var(--blue); }
.closing-section h2 { font-size: clamp(29px, 3vw, 40px); }
.closing-section .button { flex-shrink: 0; }
.site-footer { background: #f0f3f9; border-top: 1px solid var(--line); }
.footer-inner { padding-block: 34px; display: flex; align-items: center; justify-content: space-between; gap: 30px; }
.footer-brand .site-wordmark { font-size: 29px; }
.footer-brand .wordmark-chinese { font-size: 12px; }
.footer-brand p { color: var(--muted); font-size: 10px; margin-top: 12px; }
.footer-nav { display: flex; flex-wrap: wrap; align-items: center; gap: 15px 24px; font-size: 11px; color: var(--muted); }
.footer-nav a { padding-block: 10px; }
.footer-nav .admin-link { padding-left: 20px; border-left: 1px solid #cdd5e5; color: #64718a; font-size: 10px; }
html[lang="zh-CN"] h1 { font-size: clamp(46px, 5.1vw, 70px); line-height: 1.22; letter-spacing: -.04em; }
html[lang="zh-CN"] h2 { line-height: 1.32; letter-spacing: -.035em; }
html[lang="zh-CN"] .eyebrow { letter-spacing: .12em; }
html[lang="zh-CN"] .hero-description { line-height: 1.9; }
html[lang="zh-CN"] .working-copy h2 { line-height: 1.27; }
@media (min-width: 1600px) { .hero { padding-block: 105px 100px; } }
@media (max-width: 1120px) {
  .wrap { width: calc(100% - 64px); }
  .hero { gap: 35px; }
  .hero-actions { gap: 12px; }
  .product-section { gap: 50px; }
  .working-inner { gap: 65px; }
  .section-title-row { gap: 40px; }
  .section-title-row .section-description { max-width: 330px; }
  .questions-section { gap: 55px; }
  .header-nav { gap: 23px; }
}
@media (max-width: 860px) {
  .header-inner { min-height: 78px; gap: 20px; }
  .header-nav { gap: 17px; font-size: 12px; }
  .wordmark-chinese { display: none; }
  .hero { grid-template-columns: 1fr 1fr; gap: 25px; padding-block: 55px; }
  h1 { font-size: 48px; }
  html[lang="zh-CN"] h1 { font-size: 45px; }
  .hero-description { font-size: 15px; }
  .explorer { padding: 19px 17px 17px; }
  .explorer-heading h2 { font-size: 15px; }
  .explorer-controls { padding: 13px; }
  .explorer-controls label { font-size: 11px; }
  .sample-values { font-size: 10px; }
  .section-space { padding-block: 70px; }
  .product-section { grid-template-columns: 1fr; gap: 38px; }
  .section-intro { max-width: 570px; }
  .section-intro .section-description { max-width: 540px; }
  .product-features { gap: 30px 36px; }
  .working-inner { gap: 30px; grid-template-columns: .8fr 1fr; padding-block: 55px; }
  .working-copy h2 { font-size: 44px; }
  .working-example { padding: 20px; }
  .example-equation { font-size: 24px; gap: 10px; }
  .section-title-row .section-description { max-width: 285px; font-size: 14px; }
  .learning-steps { gap: 25px; }
  .learning-steps h3 { font-size: 18px; }
  .entry-option { padding: 26px; }
  .entry-option h3 { font-size: 21px; }
  .questions-section { grid-template-columns: .55fr 1.2fr; gap: 35px; padding-block: 0 55px; }
  .questions-section > h2 { font-size: 23px; }
  .footer-inner { align-items: start; }
  .footer-nav { max-width: 280px; justify-content: end; gap: 8px 17px; }
}
@media (max-width: 680px) {
  html { scroll-padding-top: 84px; }
  .wrap { width: calc(100% - 40px); }
  .header-inner { min-height: 72px; gap: 15px; }
  .site-wordmark { font-size: 31px; }
  .header-nav { margin-left: auto; }
  .header-nav a:not(:last-child) { display: none; }
  .language-link { font-size: 12px; padding-inline: 10px; gap: 7px; }
  .hero { grid-template-columns: 1fr; gap: 36px; padding-block: 45px 38px; }
  .hero-copy > .eyebrow { margin-bottom: 22px; font-size: 10px; }
  h1 { font-size: clamp(44px, 8.7vw, 58px); }
  html[lang="zh-CN"] h1 { font-size: clamp(44px, 9.5vw, 58px); }
  .hero-description { font-size: 15px; line-height: 1.8; margin-top: 22px; }
  .hero-actions { margin-top: 26px; gap: 10px 22px; }
  .hero-note { margin-top: 20px; }
  .explorer { max-width: 490px; width: 100%; margin-inline: auto; padding: 24px 21px 21px; }
  .explorer-heading h2 { font-size: 18px; }
  .explorer-controls { padding: 15px 17px 12px; }
  .explorer-controls label, .sample-values { font-size: 12px; }
  .intro-line { align-items: start; flex-direction: column; gap: 18px; padding-block: 24px; }
  .intro-line p { font-size: 14px; }
  .intro-link { font-size: 11px; gap: 19px; }
  .section-space { padding-block: 56px; }
  .product-section { gap: 33px; }
  .product-identity { margin-bottom: 24px; }
  h2 { font-size: 32px; }
  .section-description { font-size: 14px; }
  .section-intro .section-description { margin-top: 20px; }
  .product-features { gap: 29px 24px; }
  .product-features h3 { font-size: 15px; }
  .product-features p { font-size: 12px; line-height: 1.8; }
  .working-inner { grid-template-columns: 1fr; gap: 30px; padding-block: 43px; }
  .working-copy h2 { font-size: 46px; }
  .working-copy > p:last-child { margin-top: 20px; }
  .working-example { padding: 22px; }
  .example-equation { font-size: 26px; gap: 17px; }
  .section-title-row { display: block; }
  .section-title-row .eyebrow { margin-bottom: 15px; }
  .section-title-row .section-description { max-width: 450px; margin-top: 20px; }
  .learning-steps { margin-top: 28px; grid-template-columns: 1fr; gap: 26px; }
  .learning-steps li { padding-top: 18px; }
  .step-number { margin-bottom: 16px; font-size: 11px; }
  .learning-steps h3 { font-size: 19px; }
  .learning-steps p { margin-top: 10px; font-size: 13px; }
  .step-footnote { margin-top: 16px; }
  .start-section { padding-bottom: 44px; }
  .entry-options { grid-template-columns: 1fr; margin-top: 27px; gap: 17px; }
  .entry-option { padding: 26px; }
  .entry-symbol { margin-bottom: 20px; }
  .entry-option h3 { font-size: 24px; }
  .entry-option > p:not(.eyebrow):not(.entry-detail) { min-height: 0; }
  .entry-option .button { margin-top: 22px; }
  .questions-section { grid-template-columns: 1fr; gap: 20px; padding-block: 0 45px; }
  .questions-section > h2 { padding-top: 0; font-size: 23px; }
  .questions-list summary { font-size: 13px; padding-block: 19px; }
  .questions-list details p { padding-right: 15px; }
  .closing-section { display: block; padding-block: 38px 44px; }
  .closing-section h2 { font-size: 29px; }
  .closing-section .button { margin-top: 26px; }
  .footer-inner { flex-direction: column; gap: 19px; padding-block: 29px; }
  .footer-nav { max-width: none; justify-content: start; gap: 10px 21px; }
  .footer-brand .wordmark-chinese { display: inline; }
  .footer-nav .admin-link { padding-left: 16px; }
}
@media (max-width: 360px) {
  .wrap { width: calc(100% - 32px); }
  .header-nav { font-size: 11px; }
  .header-inner { gap: 10px; }
  .language-link { padding-inline: 8px; }
  h1 { font-size: 41px; }
  html[lang="zh-CN"] h1 { font-size: 40px; }
  .hero-actions { gap: 8px; }
  .product-features { grid-template-columns: 1fr; gap: 24px; }
  .explorer { padding: 19px 15px 16px; }
  .explorer-heading h2 { font-size: 16px; }
  .explorer-controls { padding: 12px; }
  .explorer-controls label, .sample-values { font-size: 11px; }
  .working-example { padding: 18px; }
  .example-equation { font-size: 23px; gap: 12px; }
  .entry-option { padding: 23px; }
}
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after { transition: none !important; animation: none !important; }
}
@media print {
  .site-header { position: static; }
  .wrap { width: 100%; }
  .hero { padding-block: 25px; }
  .section-space { padding-block: 30px; }
  .working-section { background: white; color: var(--ink); }
  .working-copy .eyebrow, .working-copy > p:last-child { color: var(--muted); }
  .working-inner { padding-block: 30px; }
  .explorer-controls, .header-nav, .language-link { display: none; }
  .entry-options, .learning-steps, .working-example { break-inside: avoid; }
}