:root{--orange:#ff7a2f;--cream:#fff8ed;--yellow:#ffd95a;--green:#91cf68;--ink:#090909;--white:#fff;--line:2px solid #090909;--rx:28px;--max:1160px}
*{box-sizing:border-box}html{scroll-behavior:smooth}body{margin:0;background:var(--cream);color:var(--ink);font-family:Inter,system-ui,-apple-system,BlinkMacSystemFont,"Segoe UI","PingFang SC","Microsoft YaHei",sans-serif;font-size:16px;line-height:1.75}a{color:inherit;text-decoration:none}button,input{font:inherit}.site{width:min(calc(100% - 20px),var(--max));margin:8px auto 24px}.notice{background:var(--orange);border:var(--line);border-radius:999px;padding:6px 12px;text-align:center;font-size:12px;font-weight:800}.header{margin-top:8px;background:var(--orange);border:var(--line);border-radius:var(--rx);padding:14px 20px;display:flex;align-items:center;gap:22px;position:sticky;top:7px;z-index:20}.brand{display:flex;align-items:center;gap:9px;font-weight:950;font-size:17px;min-width:max-content}.brand-mark{width:38px;height:38px;border:var(--line);border-radius:11px;background:var(--cream);display:grid;place-items:center;font-size:16px}.nav{display:flex;justify-content:center;gap:22px;flex:1;font-size:14px;font-weight:850}.nav a{position:relative;padding:5px 0}.nav a:after{content:"";position:absolute;left:0;right:0;bottom:0;height:2px;background:#090909;transform:scaleX(0);transform-origin:left;transition:.2s}.nav a:hover:after,.nav a.active:after{transform:scaleX(1)}.header-actions{display:flex;gap:7px}.icon-btn,.menu-btn{width:34px;height:34px;border:var(--line);border-radius:50%;background:var(--cream);display:grid;place-items:center;cursor:pointer}.menu-btn{display:none;border-radius:10px}.mobile-menu{display:none;margin-top:8px;padding:8px;background:var(--orange);border:var(--line);border-radius:18px}.mobile-menu.open{display:grid}.mobile-menu a{padding:9px 11px;border-radius:10px;font-weight:850;font-size:14px}.mobile-menu a:hover{background:var(--cream)}
.hero,.page-hero{margin-top:11px;background:var(--orange);border:var(--line);border-radius:var(--rx)}.hero{min-height:540px;padding:55px clamp(20px,5vw,62px);display:grid;grid-template-columns:1.02fr .98fr;gap:34px;align-items:center;overflow:hidden}.eyebrow{display:inline-flex;border:var(--line);border-radius:999px;background:var(--cream);padding:5px 10px;font-size:12px;font-weight:900}.hero h1,.page-hero h1{margin:15px 0 9px;font-size:clamp(44px,5.7vw,70px);line-height:.96;letter-spacing:-.055em}.hero p,.page-hero p{max-width:720px;font-size:16px;font-weight:650}.cta-row{display:flex;gap:8px;flex-wrap:wrap;margin-top:19px}.btn{display:inline-flex;align-items:center;justify-content:center;border:var(--line);border-radius:999px;padding:9px 15px;font-size:14px;font-weight:900;cursor:pointer}.btn-dark{background:var(--ink);color:var(--white)}.btn-light{background:var(--cream);color:var(--ink)}
.hero-art{min-height:340px;position:relative;display:grid;place-items:center}.pod{width:min(325px,72vw);aspect-ratio:1;background:var(--yellow);border:var(--line);border-radius:44% 56% 48% 52%;transform:rotate(-5deg);box-shadow:4px 4px #090909}.bot{position:absolute;inset:52px 58px;border:var(--line);border-radius:30px;background:var(--cream);display:flex;flex-direction:column;align-items:center;justify-content:center;box-shadow:3px 3px #090909}.bot .eyes{display:flex;gap:14px;margin-bottom:4px}.eye{width:14px;height:14px;border-radius:50%;background:#090909}.bot .digit{font-size:88px;font-weight:1000;line-height:1}.bot .name{border:var(--line);border-radius:999px;background:var(--green);padding:3px 10px;font-size:12px;font-weight:950}.speech{position:absolute;right:0;top:13px;width:155px;padding:11px;border:var(--line);border-radius:21px;background:#fff;font-size:15px;font-weight:900;box-shadow:4px 4px #090909}.speech:after{content:"";position:absolute;left:22px;bottom:-15px;width:26px;height:26px;background:#fff;border-right:var(--line);border-bottom:var(--line);transform:skew(20deg) rotate(25deg)}
.section{margin-top:11px}.section-head{display:flex;align-items:end;justify-content:space-between;gap:18px;margin:23px 6px 10px}.section-head h2{margin:0;font-size:clamp(28px,3.9vw,46px);line-height:1.02;letter-spacing:-.04em}.section-head p{margin:0;max-width:560px;font-size:14px;font-weight:650}.stats{display:grid;grid-template-columns:repeat(4,1fr);gap:10px}.card{background:#fff;border:var(--line);border-radius:21px;padding:17px;box-shadow:4px 4px #090909}.card h3{margin:0 0 4px;font-size:18px;line-height:1.3}.card p{margin:5px 0 0;font-size:14px}.stat .label{font-size:13px;font-weight:900}.stat .value{margin:8px 0 3px;font-size:32px;line-height:1.05;font-weight:1000}.stat small{font-size:11px;opacity:.65;font-weight:750}.duo{display:grid;grid-template-columns:1fr 1fr;gap:10px}.definition{background:#090909;color:#fff;border:var(--line);border-radius:var(--rx);padding:25px}.definition h2,.example h2,.tools-card h2{font-size:27px;line-height:1.12;margin:0 0 8px}.definition .formula{font-size:clamp(38px,5.6vw,60px);font-weight:1000;line-height:1;margin:12px 0 8px}.example{background:var(--yellow);border:var(--line);border-radius:var(--rx);padding:24px;box-shadow:4px 4px #090909}.example-row{display:flex;gap:9px;align-items:center;flex-wrap:wrap}.number-pill{width:53px;height:53px;background:var(--cream);border:var(--line);border-radius:13px;display:grid;place-items:center;font-size:22px;font-weight:1000}.operator{font-size:22px;font-weight:1000}.chart-shell{background:#fff;border:var(--line);border-radius:var(--rx);padding:15px;box-shadow:4px 4px #090909}.chart-toolbar{display:flex;gap:6px;flex-wrap:wrap;margin-bottom:8px}.toggle{border:var(--line);border-radius:999px;background:var(--cream);padding:5px 9px;font-size:12px;font-weight:900;cursor:pointer}.toggle.active{background:#090909;color:#fff}canvas{display:block;width:100%;height:270px}.content-grid{display:grid;grid-template-columns:1.05fr .95fr;gap:10px}.tools-card{background:var(--cream);border:var(--line);border-radius:var(--rx);padding:23px;box-shadow:4px 4px #090909}.inputs{display:grid;grid-template-columns:repeat(3,1fr);gap:8px}.input-wrap label{display:block;font-size:12px;font-weight:900;margin-bottom:3px}.input-wrap input{width:100%;padding:8px;border:var(--line);border-radius:12px;background:#fff;text-align:center;font-size:21px;font-weight:1000}.result{margin-top:11px;padding:13px;border:var(--line);border-radius:15px;background:var(--yellow)}.result .big{font-size:50px;line-height:1;font-weight:1000}.chip-row,.related{display:flex;flex-wrap:wrap;gap:6px}.chip,.related a{padding:5px 9px;border:var(--line);border-radius:999px;background:#fff;font-size:13px;font-weight:850}.note{margin-top:10px;padding:9px 11px;border:var(--line);border-radius:13px;background:var(--cream);font-size:13px;font-weight:650}.faq{display:grid;gap:7px}.faq-item{overflow:hidden;background:#fff;border:var(--line);border-radius:16px}.faq-q{width:100%;border:0;background:transparent;padding:14px 16px;display:flex;align-items:center;justify-content:space-between;gap:10px;text-align:left;font-size:15px;font-weight:900;cursor:pointer}.plus{width:28px;height:28px;border:var(--line);border-radius:50%;display:grid;place-items:center;background:var(--yellow);font-size:18px;flex:none;transition:transform .25s}.faq-a{display:grid;grid-template-rows:0fr;transition:grid-template-rows .3s}.faq-a>div{overflow:hidden}.faq-a p{margin:0;padding:0 16px 14px;font-size:14px;font-weight:650}.faq-item.open .faq-a{grid-template-rows:1fr}.faq-item.open .plus{transform:rotate(45deg)}.page-hero{padding:38px clamp(20px,5vw,55px)}.breadcrumb{margin:8px 4px 0;font-size:12px;font-weight:750;opacity:.72}.table-wrap{overflow:auto}table{width:100%;min-width:680px;border-collapse:separate;border-spacing:0;font-size:13px}th,td{padding:11px 10px;text-align:left;border-bottom:2px solid #090909}th{background:var(--yellow);font-weight:950}.seo-content{display:grid;gap:10px}.article-grid{display:grid;grid-template-columns:repeat(3,1fr);gap:10px}.mini-title{font-size:19px;font-weight:950;line-height:1.25}.footer{margin-top:11px;padding:23px;background:#090909;color:#fff;border:var(--line);border-radius:var(--rx)}.footer-grid{display:grid;grid-template-columns:1.3fr .7fr .7fr;gap:18px}.footer h3{margin:0 0 4px;font-size:17px}.footer-note{font-size:11px;opacity:.6;margin-top:12px}
@media(max-width:980px){.hero{grid-template-columns:1fr;padding:44px 27px}.hero-art{min-height:320px}.nav{gap:15px}.stats{grid-template-columns:repeat(2,1fr)}.content-grid,.duo{grid-template-columns:1fr}.article-grid{grid-template-columns:1fr 1fr}}
@media(max-width:720px){body{font-size:15px}.site{width:calc(100% - 10px);margin-top:5px}.notice{font-size:10px}.header{padding:10px 12px;border-radius:19px}.brand{font-size:14px}.brand-mark{width:33px;height:33px;font-size:14px}.nav,.header-actions{display:none}.menu-btn{display:grid;margin-left:auto}.hero,.page-hero{border-radius:19px}.hero{padding:29px 17px;min-height:auto}.hero h1{font-size:clamp(41px,13.5vw,58px)}.hero p,.page-hero p{font-size:14px}.hero-art{min-height:285px}.pod{width:min(285px,79vw)}.bot{inset:45px 53px}.bot .digit{font-size:73px}.speech{width:136px;font-size:14px;padding:9px;border-radius:18px}.section-head{display:block;margin-top:19px}.section-head p{margin-top:7px}.stats{gap:7px}.card{padding:14px;border-radius:17px;box-shadow:3px 3px #090909}.stat .value{font-size:28px}.definition,.example,.tools-card,.chart-shell{border-radius:18px;padding:19px;box-shadow:3px 3px #090909}.definition h2,.example h2,.tools-card h2{font-size:23px}.definition .formula{font-size:45px}canvas{height:225px}.article-grid{grid-template-columns:1fr}.footer{border-radius:18px;padding:19px}.footer-grid{grid-template-columns:1fr;gap:12px}}
@media(max-width:420px){.stats{grid-template-columns:1fr}.inputs{grid-template-columns:1fr}.hero-art{min-height:270px}}

/* FAQ interaction polish */
.faq-item{transition:transform .18s ease,box-shadow .18s ease}
.faq-item:hover{transform:translateY(-1px);box-shadow:3px 3px 0 var(--ink)}
.faq-q{min-height:56px}
.faq-q:focus-visible{outline:3px solid var(--yellow);outline-offset:-3px}