:root{--page:#f6fafc;--surface:#fff;--tint:#eaf6fa;--tint2:#edf4f8;--aqua:#25c8d1;--sky:#25b6e8;--blue:#1787db;--navy:#174b78;--heading:#183a56;--body:#31485d;--muted:#687d8e;--line:#dce9f0;--footer:#123653;--radius:16px}*{box-sizing:border-box}html{scroll-behavior:smooth;scroll-padding-top:30px}body{margin:0;background:var(--page);color:var(--body);font:16px/1.8 Arial,"PingFang SC","Microsoft YaHei",sans-serif;overflow-x:hidden}a{color:var(--navy);text-underline-offset:4px}a:hover{color:#086cab}a:focus-visible,button:focus-visible,summary:focus-visible{outline:3px solid var(--blue);outline-offset:3px}img{display:block;max-width:100%}.container{width:min(1180px,calc(100% - 56px));margin-inline:auto}.site-header{background:#fff;border-bottom:1px solid var(--line)}.topbar{height:72px;display:flex;align-items:center;gap:22px}.brand{display:flex;align-items:center;min-width:0;text-decoration:none;max-width:230px}.brand img{height:auto;max-height:38px;width:auto;max-width:100%;object-fit:contain}.brand-fallback{font-size:22px;font-weight:800;color:var(--navy);line-height:1.1;white-space:nowrap}.brand-fallback small{display:block;letter-spacing:2px;font-size:10px}.topbar-tagline{margin:auto;color:var(--muted);font-size:14px;letter-spacing:1px}.entry-button{background:var(--navy);color:#fff;text-decoration:none;font-size:14px;font-weight:700;padding:8px 23px;border-radius:9px;white-space:nowrap;min-height:42px;display:inline-flex;align-items:center;justify-content:center}.entry-button:hover{background:#0e629d;color:#fff}.desktop-nav{background:var(--navy)}.nav-inner{display:flex;justify-content:space-between;gap:15px}.desktop-nav a{color:#eaf7ff;text-decoration:none;padding:10px 8px 9px;min-height:48px;white-space:nowrap;font-size:14px;border-bottom:3px solid transparent}.desktop-nav a:hover,.desktop-nav a[aria-current]{color:#fff;border-bottom-color:var(--aqua);font-weight:700}.menu-toggle{display:none}.skip-link{position:absolute;left:-10000px;top:8px;z-index:50;background:white;padding:5px}.skip-link:focus{left:8px}.mobile-drawer,.drawer-overlay{visibility:hidden;pointer-events:none}.mobile-bottom{display:none}.section{padding-block:54px}.section--white{background:#fff}.section--tint{background:var(--tint)}.section-head{margin-bottom:25px}.eyebrow{color:#147aa2;text-transform:uppercase;letter-spacing:1.5px;font-size:12px;font-weight:800}.section-head h2,h2{color:var(--heading);line-height:1.4}h1,h2,h3,p{margin-top:0}h1{font-size:40px;line-height:1.35;letter-spacing:-.7px;color:var(--heading);margin-bottom:22px}h2{font-size:26px;margin-bottom:18px}h3{font-size:20px;line-height:1.45;color:var(--heading);margin-bottom:10px}p{margin-bottom:18px}.lead{font-size:17px;line-height:1.85;color:#446079}.muted{color:var(--muted)}.home-hero{display:grid;grid-template-columns:56fr 44fr;align-items:center;gap:38px;padding-block:52px 42px}.home-hero .hero-copy p{max-width:615px}.hero-actions{display:flex;gap:13px;flex-wrap:wrap;margin-top:24px}.btn{display:inline-flex;align-items:center;text-decoration:none;min-height:44px;padding:8px 20px;font-weight:700;border-radius:10px}.btn--primary{color:#fff;background:linear-gradient(115deg,#1487c8,#159fac)}.btn--primary:hover{color:#fff;background:var(--navy)}.btn--light{background:#fff;border:1px solid var(--line)}.media{display:flex;justify-content:center;align-items:center;width:100%;min-width:0;overflow:hidden;background:var(--tint);border-radius:14px}.media img{display:block;width:auto;height:auto;max-width:100%;max-height:100%;object-fit:contain;object-position:center}.media--hero{height:clamp(250px,26vw,330px)}.media--feature{height:250px}.media--card{height:170px}.media--banner{height:220px}.media--mobile{height:350px;max-width:320px}.media--portrait{max-width:370px;margin-inline:auto}.media--placeholder{background:linear-gradient(135deg,#eaf6fa,#edf4f8);border:1px solid #e2edf2}.home-shortcuts{border-top:1px solid var(--line);background:#fff;padding:15px 0}.shortcuts-inner{display:flex;gap:30px;flex-wrap:wrap;font-size:13px}.shortcuts-inner div{display:flex;gap:10px;flex-wrap:wrap}.shortcuts-inner strong{color:var(--heading)}.shortcuts-inner a{text-decoration:none;border-bottom:1px solid #b8dce9}.topic-grid{display:grid;grid-template-columns:repeat(4,minmax(0,1fr));gap:16px}.topic-card{display:flex;flex-direction:column;gap:10px;text-decoration:none;color:var(--body);padding:23px;background:#fff;border:1px solid var(--line);border-radius:var(--radius);transition:border-color .2s,transform .2s}.topic-card:hover{border-color:var(--sky);transform:translateY(-2px)}.topic-card strong{color:var(--heading);font-size:18px;line-height:1.5}.topic-card span{font-size:14px;line-height:1.75}.text-arrow{margin-top:auto;color:#1676a0;font-weight:700}.feature-split{display:grid;grid-template-columns:2fr 1fr;gap:22px}.feature-split article,.mini-feature,.paper-card,.rules-card{background:#fff;border:1px solid var(--line);border-radius:var(--radius);padding:25px}.feature-split aside{display:grid;gap:20px}.feature-split h3{font-size:21px}.feature-split a,.paper-card a{font-weight:700}.editorial-row{display:grid;grid-template-columns:1fr 1fr;align-items:center;gap:45px}.editorial-row.reverse .media{order:-1}.editorial-row .media{min-width:0}.rule-preview{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:17px}.rule-preview>article{padding:23px;border-top:4px solid var(--aqua);background:white;border-radius:0 0 12px 12px}.rule-preview b{font-size:18px;color:var(--navy)}.steps{display:grid;grid-template-columns:repeat(4,minmax(0,1fr));gap:15px;counter-reset:step}.steps>div{background:#fff;border-left:3px solid var(--aqua);padding:17px;border-radius:6px;counter-increment:step}.steps>div:before{content:"0" counter(step);font-size:12px;font-weight:800;color:#0b82a4;display:block}.page-top{padding-top:49px;padding-bottom:24px}.page-top h1{font-size:34px}.page-top .lead{max-width:850px}.reading-shell{padding-bottom:56px}.article-section{margin-top:37px}.article-section h2{margin-bottom:17px}.article-section p{max-width:780px}.article-section ul,.article-section ol{padding-left:24px}.article-section li{margin-bottom:9px}.article-narrow{max-width:780px}.prose-grid{display:grid;grid-template-columns:1fr 1fr;gap:22px}.prose-grid>article{padding:24px;border:1px solid var(--line);background:#fff;border-radius:13px;min-width:0}.scroll-table{overflow-x:auto;border-radius:12px;border:1px solid var(--line);background:#fff}table{border-collapse:collapse;width:100%;min-width:570px;text-align:left}th,td{padding:13px 17px;vertical-align:top;border-bottom:1px solid var(--line)}th{background:#eaf6fa;color:var(--heading);font-weight:700}tr:last-child td{border-bottom:0}.timeline{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:16px}.timeline article{border-top:4px solid var(--sky);background:#fff;padding:23px;border-radius:7px}.football-layout{display:grid;grid-template-columns:minmax(0,760px) minmax(0,240px);gap:52px;align-items:start}.aside-panel{background:var(--tint);padding:22px;border-radius:12px;position:sticky;top:20px}.aside-panel h2{font-size:19px}.aside-panel dl{margin:0}.aside-panel dt{font-weight:700;color:var(--heading);margin-top:14px}.aside-panel dd{margin-left:0;font-size:14px}.article-figure{margin-block:24px}.article-figure figcaption{text-align:center;color:var(--muted);font-size:13px;margin-top:9px}.numbered{counter-reset:seq}.numbered article{padding:18px 0 18px 54px;border-bottom:1px solid var(--line);counter-increment:seq;position:relative}.numbered article:before{content:counter(seq,decimal-leading-zero);position:absolute;left:0;top:16px;color:#119cb3;font-size:24px;font-weight:800}.matrix{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:18px}.matrix article{padding:23px;border-radius:14px;background:#fff;border:1px solid var(--line)}.matrix ul{padding-left:19px}.matrix li{margin-bottom:7px}.gallery{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:22px}.gallery figure{margin:0;background:#fff;border:1px solid var(--line);border-radius:14px;padding:18px;min-width:0}.gallery figcaption{padding:15px 3px 0}.gallery figcaption strong{color:var(--heading);display:block}.side-by-side{display:grid;grid-template-columns:1.4fr 1fr;align-items:center;gap:30px}.section-index{display:flex;flex-wrap:wrap;gap:11px;padding:14px 0}.section-index a{padding:6px 14px;border:1px solid #bbd9e3;border-radius:8px;background:white;text-decoration:none;font-size:14px}.faq{border-bottom:1px solid var(--line);padding:1px 0}.faq summary{cursor:pointer;color:var(--heading);font-weight:700;padding:15px 22px 15px 2px}.faq p{padding:0 20px 10px 2px;margin:0}.service-table{width:100%}.note{background:#eaf6fa;border-left:4px solid var(--aqua);padding:18px 23px;border-radius:4px;margin:26px 0}.related{border-top:1px solid var(--line);margin-top:50px;padding-top:28px}.related-list{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:13px}.related-list a{padding:15px;border:1px solid var(--line);background:white;border-radius:10px;text-decoration:none;font-weight:700}.site-footer{background:var(--footer);color:#eaf7ff;padding:42px 0 23px}.site-footer p{color:#d8e7ee;max-width:440px;font-size:14px}.footer-grid{display:grid;grid-template-columns:1fr 1fr;gap:38px}.site-footer strong{font-size:21px}.site-footer strong small{font-size:11px;letter-spacing:1px}.site-footer h2{color:white;font-size:18px}.footer-links{display:flex;flex-wrap:wrap;gap:10px 19px}.footer-links a{color:#eaf7ff;font-size:14px}.footer-note{font-size:12px;color:#c6d8e5;border-top:1px solid #38617b;padding-top:20px;margin-top:25px}.back-to-top{position:fixed;right:20px;bottom:20px;border:0;border-radius:50%;height:42px;width:42px;cursor:pointer;background:var(--navy);color:white;font-size:22px;opacity:0;pointer-events:none;transition:opacity .2s}.back-to-top.is-visible{opacity:1;pointer-events:auto}@media(max-width:980px){.container{width:min(100% - 44px,1180px)}.topbar{height:64px;justify-content:space-between;gap:10px}.menu-toggle{display:flex;width:40px;height:40px;flex-direction:column;justify-content:center;align-items:center;gap:5px;border:1px solid var(--line);background:white;border-radius:9px;flex-shrink:0;cursor:pointer}.menu-toggle span{width:18px;height:2px;background:var(--heading)}.brand{position:absolute;left:50%;transform:translateX(-50%);max-width:40vw;justify-content:center}.brand img{max-height:30px}.brand-fallback{font-size:17px}.brand-fallback small{font-size:8px}.topbar-tagline,.desktop-nav{display:none}.entry-button{height:40px;min-height:40px;padding:7px 13px;font-size:13px}.drawer-overlay{display:block;position:fixed;inset:0;background:rgba(16,42,60,.48);z-index:90;opacity:0;transition:opacity .2s}.mobile-drawer{display:block;position:fixed;left:0;top:0;bottom:0;z-index:91;width:min(86vw,344px);background:#fff;overflow-y:auto;transform:translateX(-102%);transition:transform .2s;box-shadow:6px 0 30px #17375022}.drawer-open{overflow:hidden}.drawer-open .drawer-overlay,.drawer-open .mobile-drawer{visibility:visible;pointer-events:auto}.drawer-open .drawer-overlay{opacity:1}.drawer-open .mobile-drawer{transform:translateX(0)}.drawer-head{display:flex;align-items:center;justify-content:space-between;padding:16px 20px;border-bottom:1px solid var(--line)}.drawer-close{height:40px;width:40px;font-size:30px;color:var(--heading);border:0;background:var(--tint);cursor:pointer}.drawer-group{padding:13px 20px;border-bottom:1px solid var(--line)}.drawer-group b{display:block;color:var(--muted);font-size:12px;margin-bottom:6px}.drawer-group a{display:block;padding:10px 0;color:var(--heading);text-decoration:none;font-weight:700}.home-hero{gap:23px}.topic-grid{grid-template-columns:repeat(2,minmax(0,1fr))}.football-layout{grid-template-columns:minmax(0,1fr)}.aside-panel{position:static}.section{padding-block:40px}}@media(max-width:760px){.home-hero{grid-template-columns:1fr;padding-block:32px}.home-hero .media{grid-row:1}.editorial-row,.feature-split,.side-by-side{grid-template-columns:1fr}.feature-split aside{grid-template-columns:1fr 1fr}.editorial-row.reverse .media{order:0}.timeline,.matrix,.rule-preview,.steps{grid-template-columns:1fr 1fr}.footer-grid{grid-template-columns:1fr}.prose-grid{grid-template-columns:1fr}.related-list{grid-template-columns:1fr 1fr}}@media(max-width:640px){body{font-size:15px;line-height:1.78}.container{width:calc(100% - 32px)}h1{font-size:29px}.page-top h1{font-size:27px}h2{font-size:22px}h3{font-size:18px}.lead{font-size:16px}.section{padding-block:32px}.page-top{padding-top:30px;padding-bottom:10px}.topic-grid,.timeline,.matrix,.rule-preview,.steps,.gallery,.related-list,.feature-split aside{grid-template-columns:1fr}.topic-card{padding:18px}.feature-split article,.mini-feature,.paper-card,.rules-card,.prose-grid>article{padding:19px}.media--hero{height:200px}.media--feature{height:180px}.media--card{height:145px}.media--banner{height:150px}.media--mobile{height:290px;max-width:250px}.shortcuts-inner{gap:11px}.shortcuts-inner>div{width:100%}.section-index{gap:7px}.section-index a{font-size:13px;padding:5px 8px}.mobile-bottom{display:grid;grid-template-columns:repeat(4,1fr);position:fixed;bottom:0;left:0;right:0;z-index:70;padding-bottom:env(safe-area-inset-bottom,0px);background:#fff;border-top:1px solid var(--line);box-shadow:0 -3px 12px #12365312}.mobile-bottom a{text-align:center;text-decoration:none;font-size:13px;font-weight:700;color:var(--body);padding:11px 0}.mobile-bottom a[aria-current]{color:var(--blue);border-top:3px solid var(--aqua);padding-top:8px}body{padding-bottom:calc(48px + env(safe-area-inset-bottom,0px))}.back-to-top{bottom:75px}.site-footer{padding-bottom:28px}}@media(max-height:480px) and (max-width:640px){.mobile-bottom{position:static}body{padding-bottom:0}.back-to-top{bottom:15px}}@media(prefers-reduced-motion:reduce){html{scroll-behavior:auto}*,*:before,*:after{animation-duration:.01ms!important;transition-duration:.01ms!important}}

.noscript-nav{display:none}@media(max-width:980px){.noscript-nav{display:block;background:#eaf6fa;border-bottom:1px solid #dce9f0}.noscript-nav .container{display:flex;flex-wrap:wrap;gap:4px 15px;padding-block:10px}.noscript-nav a{font-size:13px;font-weight:700}}