*{box-sizing:border-box}html{scroll-behavior:smooth}body{margin:0;background:#f6f8fc;color:#152a40;font:16px/1.65 system-ui,-apple-system,"Segoe UI",sans-serif}a{color:inherit}.wrap{width:min(1180px,calc(100% - 36px));margin:auto}.skip{position:fixed;top:-100px;left:20px;background:#fff;padding:12px;z-index:50}.skip:focus{top:12px}.site-header{position:sticky;top:0;z-index:30;background:#102a45;color:#fff;box-shadow:0 8px 28px #05152522}.masthead{display:flex;align-items:center;gap:22px;justify-content:space-between;min-height:76px}.brand{white-space:nowrap;text-decoration:none;font-size:1.4rem;font-weight:850;letter-spacing:-.045em}.brand-dot{color:#86eadc}.site-menu,.primary-links,.language-switch{display:flex;align-items:center;gap:15px}.site-menu{flex:1;justify-content:space-between}.primary-links a{padding:9px 12px;text-decoration:none;font-weight:650;border-radius:8px}.primary-links a:hover,.primary-links a:focus-visible{background:#ffffff1d}.language-switch label{white-space:nowrap;font-weight:650}.language-switch select{background:#fff;color:#14283e;border:0;border-radius:9px;padding:10px 8px;max-width:144px;font:inherit}.menu-toggle{display:none;background:transparent;border:1px solid #ffffff70;border-radius:10px;width:46px;height:44px;padding:9px;cursor:pointer}.menu-toggle span{display:block;background:white;height:2px;width:100%;margin:5px 0;border-radius:2px}.hero{background:radial-gradient(circle at 85% 20%,#1f7693 0%,transparent 36%),linear-gradient(125deg,#102a45,#124e6d);color:#fff;padding:90px 0 96px}.hero-layout{display:grid;grid-template-columns:1.35fr .65fr;align-items:center;gap:40px}.eyebrow,.section-kicker{font-size:.77rem;font-weight:800;letter-spacing:.15em;text-transform:uppercase;color:#2a7881}.hero .eyebrow{color:#9af2e2}.hero h1{max-width:800px;font-size:clamp(2.3rem,6vw,4.8rem);line-height:1.08;letter-spacing:-.055em;margin:22px 0}.hero p{font-size:1.16rem;color:#e4f4fc;max-width:600px}.hero-ctas{display:flex;gap:12px;flex-wrap:wrap;margin-top:28px}.btn{display:inline-block;background:#f9ce5b;color:#102a45;padding:11px 19px;border-radius:11px;font-weight:800;text-decoration:none;border:2px solid transparent}.btn:hover{filter:brightness(.95)}.btn-ghost{background:transparent;border-color:#ffffff8a;color:white}.btn-outline{background:#0a6280;color:white;border:0;text-align:center;margin-top:auto}.hero-art{display:grid;grid-template-columns:1fr 1fr;gap:12px;transform:rotate(7deg)}.hero-art span{display:grid;place-items:center;min-height:135px;background:#ffffff16;border:1px solid #ffffff3e;border-radius:24px;font-size:4rem;font-weight:900;color:#b2f9eb}.hero-art span:nth-child(2){color:#f9ce5b}.section{padding:65px 0 10px}.section-head{display:flex;justify-content:space-between;align-items:end;gap:12px;margin-bottom:24px}.section-head a{font-weight:700;color:#075d7c}.section h2,.about h2,.guide h2{font-size:clamp(1.6rem,3vw,2.25rem);line-height:1.25;letter-spacing:-.03em;margin:8px 0}.section-head p{color:#4a6275;margin:9px 0}.course-grid,.app-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(230px,1fr));gap:16px}.course-card,.app-card{background:white;border:1px solid #dce6ee;border-radius:17px;box-shadow:0 8px 25px #142e4608;padding:23px}.course-card{text-decoration:none;min-height:170px;display:flex;flex-direction:column;gap:13px;transition:transform .15s}.course-card:hover,.course-card:focus-visible{transform:translateY(-3px);border-color:#0e698d}.course-card strong{font-size:1.07rem;line-height:1.3}.course-card>span:last-child{margin-top:auto;color:#126b85;font-size:.9rem}.course-mark{font-size:1.5rem;color:#20809b}.app-card{display:flex;flex-direction:column;min-height:250px}.app-card[hidden]{display:none}.app-symbol{font-size:2rem}.app-card h3{line-height:1.3}.app-card p{color:#536b7b;flex:1}.search-label{font-weight:750;display:block}.search-label+input{width:min(100%,520px);padding:12px 14px;border:1px solid #9bb2be;border-radius:10px;font:inherit;margin:8px 0 24px}.about,.guide{margin:55px 0;background:#e9f2f8;padding:28px;border-radius:17px}.breadcrumbs{padding:23px 0;color:#496477;font-size:.9rem;display:flex;flex-wrap:wrap;gap:8px}.breadcrumbs a{color:#135e7d}.page-intro{padding:45px 0 25px;max-width:900px}.page-intro h1{font-size:clamp(2rem,5vw,3.6rem);line-height:1.15;letter-spacing:-.04em}.page-intro p{color:#405c71;font-size:1.1rem;max-width:750px}.guide ol{padding-left:22px}.guide a{color:#075d7c;font-weight:750}footer{background:#102a45;color:#e3f0f8;padding:34px 0;margin-top:72px}footer p{font-size:.9rem;color:#b7d0dd}a:focus-visible,button:focus-visible,select:focus-visible,input:focus-visible{outline:3px solid #f4bf44;outline-offset:3px}@media(max-width:950px){.menu-toggle{display:block}.masthead{flex-wrap:wrap;min-height:68px;padding:12px 0}.site-menu{display:none;flex-basis:100%;flex-direction:column;align-items:stretch;gap:12px;padding:15px 0 8px;border-top:1px solid #ffffff40}.site-menu.is-open{display:flex}.primary-links{flex-direction:column;align-items:stretch;gap:3px}.primary-links a{display:block;padding:12px}.language-switch{padding:12px;flex-wrap:wrap;border-top:1px solid #ffffff30;justify-content:space-between}.language-switch select{max-width:190px}.hero{padding:55px 0}.hero-layout{grid-template-columns:1fr}.hero-art{display:none}}@media(max-width:520px){.wrap{width:min(100% - 26px,1180px)}.hero h1{font-size:2.5rem}.section{padding-top:44px}.course-grid,.app-grid{grid-template-columns:1fr}.section-head{align-items:start;flex-direction:column}.page-intro{padding:24px 0}}@media(prefers-reduced-motion:reduce){html{scroll-behavior:auto}.course-card{transition:none}}
.lesson-section{margin:48px 0 15px;padding:32px;background:#fff;border:1px solid #dce6ee;border-radius:18px}.lesson-section h2{font-size:clamp(1.45rem,3vw,2rem);line-height:1.25}.lesson-eyebrow{font-size:.8rem;text-transform:uppercase;letter-spacing:.08em;color:#075d7c;font-weight:800}.worked-example{padding:18px 22px;border-left:4px solid #0e7897;border-radius:8px;background:#edf7fa;margin:22px 0}.worked-example h3{margin:0}.math-question{font-size:1.18rem;font-weight:750;overflow-wrap:anywhere}.practice-grid{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:14px}.practice-card{background:#f7f9fb;border:1px solid #d5e5eb;border-radius:13px;padding:16px;min-width:0}.practice-card h3{margin:0}.practice-card summary{cursor:pointer;color:#075d7c;font-weight:750;padding:9px 0}.practice-card details p{border-top:1px solid #c3d9e5;padding-top:10px}.learning-tip{padding:15px;background:#fff7e4;border-radius:10px}@media(max-width:730px){.practice-grid{grid-template-columns:1fr}.lesson-section{padding:19px}}
/* v5 lesson engine, donations and laboratories */
.donation-panel{margin:0 0 1.5rem;padding:1.25rem 1.5rem;border:1px solid #789aab;border-radius:16px;background:#f0f8f8;color:#102a45;max-width:740px}.donation-panel h2{font-size:1.35rem;margin:.1rem 0 .5rem;color:#102a45}.donation-panel p{color:#264c58;margin:.3rem 0 1rem}.paypal-donation{min-height:50px}.interactive-exercises,.lab-section{margin:2rem 0;padding:clamp(1rem,3vw,2rem);border:1px solid #d2e2e9;border-radius:18px;background:#f5fafc;color:#142e44}.interactive-exercises h2,.lab-section h2{color:#142e44}.quiz-tools{display:flex;gap:1rem;align-items:end;flex-wrap:wrap}.quiz-tools label,.lab-card label{display:grid;gap:.3rem;font-weight:700}.quiz-tools select,.quiz-question input{border:1px solid #809dad;border-radius:8px;padding:.65rem .8rem;font-size:1rem;background:white;color:#142e44}.quiz-stats{font-weight:700;color:#08595e}.quiz-list{display:grid;grid-template-columns:repeat(auto-fit,minmax(min(100%,290px),1fr));gap:1rem;margin:1.2rem 0}.quiz-question{border:1px solid #c5d9df;border-radius:12px;background:white;padding:1.1rem;display:grid;gap:.75rem;align-content:start}.quiz-question label{font-weight:600;display:grid;gap:.65rem}.quiz-question button{justify-self:start}.quiz-feedback{margin:0;min-height:1.5rem}.quiz-feedback.correct{color:#0f6c3a;font-weight:bold}.quiz-feedback.incorrect{color:#9b3328}.quiz-reset{background:transparent;border:0;text-decoration:underline;cursor:pointer;color:#075b65;padding:.5rem}.labs-grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(min(100%,330px),1fr));gap:1rem}.lab-card{padding:1.2rem;border-radius:12px;background:white;border:1px solid #d0e0e8;display:grid;gap:1rem;min-width:0}.lab-card input[type=range]{width:100%;accent-color:#007a80}.lab-output{font-size:1.4rem;font-weight:700;color:#065f67}.number-track{height:14px;border-radius:12px;background:linear-gradient(90deg,#d4e2ed,#93c5c8);position:relative;margin:1.2rem .4rem}.number-dot{position:absolute;top:-8px;width:24px;height:30px;background:#006b73;border-radius:9px;transform:translateX(-50%)}.lab-card canvas{display:block;width:100%;height:auto;border:1px solid #c5d6e3;border-radius:8px}.btn-small{padding:.5rem .85rem;font-size:.9rem}@media(max-width:680px){.quiz-tools{align-items:stretch;flex-direction:column}.quiz-tools>*{width:100%}.quiz-question{padding:.9rem}}

/* v6 editorial redesign: neutral, airy, accessible */
:root{--ink:#17263a;--muted:#566778;--line:#dce4e9;--accent:#286779;--bg:#f8fafb}
body{background:var(--bg);color:var(--ink);font-family:Inter,"Segoe UI",system-ui,sans-serif}
.site-header,footer{background:#162a39;box-shadow:none}.masthead{min-height:72px}
.brand{display:flex;align-items:center;gap:11px;font-size:1.35rem;letter-spacing:-.04em}.brand-logo{display:inline-grid;place-items:center;height:35px;width:35px;border-radius:10px;background:#a5c8cb;color:#112c39;font-size:1.3rem;font-weight:900}.brand-dot{color:#a2cace}
.primary-links a{font-weight:600;font-size:.92rem}.site-header .primary-links a:hover{background:#345060}
.hero{background:linear-gradient(130deg,#182e3d 15%,#2b5260 92%);padding:80px 0 82px}
.hero-layout{grid-template-columns:1.3fr .7fr;gap:60px}.hero h1{font-size:clamp(2.7rem,5.2vw,5rem);font-weight:790;letter-spacing:-.055em;margin:14px 0 22px}.hero p{font-size:1.16rem;color:#e1e8eb;line-height:1.7}.eyebrow{letter-spacing:.18em;font-size:.72rem}.hero .eyebrow{color:#c7dedf}.hero-art{transform:none;display:grid;grid-template-columns:1fr 1fr;gap:13px;align-items:stretch}.hero-art .orbit{min-height:110px;border:1px solid #d4e6e550;background:#ffffff0c;border-radius:16px;display:grid;place-items:center;font-size:.9rem;font-weight:750;letter-spacing:.12em;color:#dce7e9}.hero-art .orbit:nth-child(2){background:#aac5c51a}.hero-art .orbit:nth-child(3){background:#aec6bb1f}.hero-art .orbit:nth-child(4){background:#e7dfce16}
.btn{background:#c9dddb;color:#163040;border-radius:9px;font-size:.94rem}.btn-ghost{background:transparent;color:#fff;border-color:#a4b8c4}.section{padding:62px 0 16px}.section-kicker{color:#4b7880}.section-head{align-items:start}.section-head h2{font-size:clamp(2rem,3.5vw,2.7rem);font-weight:760}.section-head p{max-width:700px;color:#566a78}.search-label{font-size:.9rem;color:#455d69}.search-label+input{border:1px solid #c6d6dc;background:#fff;box-shadow:none;border-radius:10px;max-width:560px;margin-bottom:16px}.filter-row{display:flex;gap:9px;flex-wrap:wrap;margin:0 0 28px}.filter-chip{border:1px solid #cfdde0;border-radius:30px;padding:8px 16px;background:#fff;color:#415665;font:600 .9rem system-ui;cursor:pointer}.filter-chip.active,.filter-chip:hover{background:#254c5a;border-color:#254c5a;color:white}.app-grid{grid-template-columns:repeat(auto-fit,minmax(240px,1fr));gap:19px}.app-card{border:1px solid var(--line);box-shadow:0 4px 14px #15293b08;background:white;border-radius:16px;padding:23px;min-height:255px;transition:box-shadow .2s,transform .2s}.app-card:hover{box-shadow:0 15px 32px #18314315;transform:translateY(-3px)}.app-card-top{display:flex;align-items:center;justify-content:space-between;gap:8px}.app-symbol{display:grid;place-items:center;width:64px;height:64px;border-radius:16px;background:#edf3f4;color:#34566a;font-size:1.05rem;font-weight:850;letter-spacing:-.035em}.bio .app-symbol,.chem .app-symbol{background:#e9f2ec;color:#316b50}.physics .app-symbol,.math .app-symbol{background:#e9eff6;color:#315981}.lang .app-symbol,.eng .app-symbol{background:#f4eee8;color:#895e41}.art .app-symbol,.history .app-symbol{background:#f0eaf2;color:#6e5279}.level-tag{color:#62737c;font-size:.72rem;text-align:right;max-width:150px;line-height:1.3}.app-card h3{font-size:1.2rem;line-height:1.3;letter-spacing:-.03em;margin:20px 0 2px}.app-card p.program-name{font-size:.9rem;color:#687d89;margin:0 0 22px;flex:1}.course-open{text-decoration:none;font-weight:750;color:#245d70;font-size:.91rem;display:inline-flex;align-items:center}.course-open:hover{text-decoration:underline}.donation-panel{background:#edf4f3;border-color:#c8d9d9}footer .donation-panel p{color:#345461}.about{background:#ecf3f4}.course-card{box-shadow:none}
@media(max-width:950px){.hero-layout{grid-template-columns:1fr}.hero-art{display:none}}
@media(max-width:520px){.hero{padding:55px 0}.hero h1{font-size:2.65rem}.filter-chip{font-size:.85rem;padding:8px 12px}.app-grid{grid-template-columns:1fr}.app-card{min-height:220px}.site-menu.is-open{max-height:calc(100dvh - 76px);overflow:auto}}
@media(prefers-reduced-motion:reduce){.app-card{transition:none}.app-card:hover{transform:none}}

/* v8: native HTML language links, no JS required */
.lang-menu{position:relative;min-width:160px}.lang-menu summary{list-style:none;cursor:pointer;background:#fff;color:#16354b;padding:9px 13px;border-radius:10px;font-weight:750;white-space:nowrap}.lang-menu summary::-webkit-details-marker{display:none}.lang-list{position:absolute;right:0;top:calc(100% + 8px);width:190px;padding:6px;background:#fff;color:#153247;border:1px solid #cbdce8;border-radius:12px;box-shadow:0 12px 30px #081d3540;z-index:99}.lang-list a{display:block;padding:9px 12px;text-decoration:none;border-radius:7px}.lang-list a:hover,.lang-list a:focus-visible,.lang-list a[aria-current="page"]{background:#e5f1f7;color:#075670}@media(max-width:950px){.lang-menu,.lang-menu summary{width:100%}.lang-list{position:static;width:100%;margin-top:8px;box-shadow:none}}

/* v9 privacy and legal: accessible neutral surfaces */
.legal-links{display:flex;gap:1rem;flex-wrap:wrap;align-items:center;margin:1.25rem 0}.legal-links a,.legal-links button{color:inherit;text-decoration:underline}.legal-links button{cursor:pointer;background:none;border:0;font:inherit;padding:.2rem}.legal-article{max-width:830px;margin:3rem auto;padding:1.5rem 2rem;background:var(--surface,#fff);color:var(--text,#263746);border:1px solid #a9b5be;border-radius:14px;line-height:1.7}.legal-article h1{font-size:clamp(1.7rem,4vw,2.5rem)}.legal-article h2{font-size:1.2rem;margin-top:1.8rem}.privacy-overlay:not([hidden]){position:fixed;inset:0;z-index:99999;background:rgba(17,29,40,.78);display:grid;place-items:center;padding:1rem}.privacy-overlay[hidden]{display:none!important}.privacy-dialog{background:#fff;color:#172b3b;width:min(100%,610px);max-height:88vh;overflow:auto;box-shadow:0 16px 50px #0006;border-radius:16px;padding:clamp(1.25rem,3vw,2rem);line-height:1.55}.privacy-dialog h2{font-size:1.5rem;margin-top:0}.privacy-dialog a{color:#08457a}.privacy-actions{display:flex;gap:.6rem;flex-wrap:wrap;margin:1rem 0}.privacy-actions button,.locale-btn,.paypal-launch{cursor:pointer;font:inherit;padding:.75rem 1rem;border:1px solid #49697b;border-radius:9px;background:#eaf1f5;color:#163244;min-height:44px}.privacy-actions button:first-child{background:#173f5d;color:white}.consent-opt{display:block;margin:1rem 0}.locale-panel{margin:2rem auto;padding:1.3rem;border:1px solid #96a5ae;border-radius:14px;max-width:1050px}.locale-panel button{margin:.3rem}.locale-panel h2{font-size:1.2rem}@media(max-width:480px){.privacy-actions button{width:100%}.legal-article{margin:1rem;padding:1.1rem}}