:root{--navy:#131e35;--cyan:#00b8c5;--white:#fff;--ink:#17213a;--muted:#667085;--line:#dde5ea;--soft:#f6fafb;--softcyan:#edfafa;--radius:18px;--shadow:0 10px 30px rgba(19,30,53,.07)}
*{box-sizing:border-box}html{scroll-behavior:smooth}body{margin:0;font-family:Poppins,system-ui,sans-serif;color:var(--navy);background:#fff;line-height:1.55}a{text-decoration:none;color:inherit}img{max-width:100%;display:block}svg{width:1.35em;height:1.35em}.container{width:min(1180px,calc(100% - 40px));margin:auto}.section{padding:38px 0}.section.compact{padding:28px 0}.section-title{font-family:Alexandria,sans-serif;font-size:clamp(1.5rem,2.2vw,2rem);text-align:center;margin:0 0 24px;font-weight:700}.btn{display:inline-flex;align-items:center;justify-content:center;min-height:42px;padding:0 18px;border-radius:10px;font-weight:600;font-size:.9rem;border:1px solid transparent;transition:.2s}.btn-cyan{background:var(--cyan);color:#fff}.btn-cyan:hover{transform:translateY(-1px);box-shadow:0 8px 18px rgba(0,184,197,.25)}.btn-outline{border-color:#cfd8df;background:#fff}.btn-outline:hover{border-color:var(--navy)}
/* Brand */
.brand-logo{display:inline-flex;align-items:center;gap:12px;white-space:nowrap}.brand-logo .natscix{font-family:Alexandria,sans-serif;font-weight:900;font-size:31px;letter-spacing:-1.8px;color:var(--navy);line-height:1}.brand-logo .bar{height:25px;width:1.5px;background:var(--cyan)}.brand-logo .learn{font-family:Poppins,sans-serif;font-weight:600;letter-spacing:.42em;font-size:13px;color:var(--cyan);padding-left:.2em}.brand-logo.on-dark .natscix{color:#fff}.brand-compact{display:inline-flex;flex-direction:column;background:var(--navy);border-radius:13px;padding:10px 14px;line-height:1}.brand-compact .scix{font-family:Alexandria,sans-serif;font-size:24px;font-weight:900;color:#fff;letter-spacing:-1px}.brand-compact .learn{font-family:Poppins,sans-serif;color:var(--cyan);font-size:8px;letter-spacing:.36em;margin-top:7px;font-weight:600}
/* Header */
.site-header{position:sticky;top:0;z-index:50;background:rgba(255,255,255,.95);backdrop-filter:blur(14px);border-bottom:1px solid #edf0f3}.header-inner{height:72px;display:flex;align-items:center;gap:28px}.logo-link{display:flex;align-items:center}.desktop-nav{display:flex;align-items:center;gap:28px;margin-left:auto}.desktop-nav a{font-size:.88rem;font-weight:500}.desktop-nav a:hover{color:var(--cyan)}.header-actions{display:flex;align-items:center;gap:10px}.icon-link{display:grid;place-items:center;width:42px;height:42px}.menu-btn{display:none;border:0;background:none;padding:8px}.menu-btn span{display:block;width:22px;height:2px;background:var(--navy);margin:4px}.mobile-menu{display:none}
/* Hero */
.hero{padding-top:44px}.hero-grid{display:grid;grid-template-columns:1.03fr .97fr;gap:48px;align-items:center}.hero h1{font-family:Alexandria,sans-serif;font-size:clamp(2.8rem,5.2vw,5.1rem);line-height:1.03;letter-spacing:-.045em;margin:0 0 18px;max-width:700px}.hero-sub{font-size:1rem;color:#586174;max-width:590px;margin-bottom:22px}.searchbar{height:58px;border:1px solid #ccd7df;border-radius:12px;display:flex;align-items:center;padding:0 18px;gap:12px;background:#fff;box-shadow:0 6px 18px rgba(19,30,53,.04)}.searchbar span{display:grid;place-items:center;color:#40506a}.searchbar input{border:0;outline:0;flex:1;font-family:Poppins;font-size:.95rem;color:var(--navy)}.chips{display:flex;flex-wrap:wrap;gap:8px;margin:12px 0 18px}.chips a{font-size:.72rem;padding:7px 10px;border:1px solid #dbe4e8;border-radius:999px;background:#fff;color:#5c6576}.chips a:hover{border-color:var(--cyan);color:var(--navy)}.selectors{display:grid;grid-template-columns:repeat(4,1fr);gap:10px}.selector{height:52px;border:1px solid #d7e0e5;border-radius:11px;display:flex;align-items:center;justify-content:center;font-size:.82rem;font-weight:600}.selector.active{border:1.5px solid var(--cyan);box-shadow:inset 0 0 0 1px #c4f1f3}.hero-art{height:390px;position:relative;border-radius:40px;overflow:hidden;background:linear-gradient(145deg,#f7fbfc 0%,#edf7f8 100%)}.hero-art .orb{position:absolute;width:360px;height:360px;border-radius:50%;background:#eef6fb;right:18px;top:15px}.book-stack{position:absolute;left:35px;bottom:68px;width:180px;transform:rotate(-4deg)}.book-stack i{display:block;height:34px;border-radius:6px;margin-top:-3px;box-shadow:0 7px 15px rgba(19,30,53,.14)}.book-stack i:nth-child(1){background:#00b8c5;width:160px;margin-left:14px}.book-stack i:nth-child(2){background:#1d355c;width:175px}.book-stack i:nth-child(3){background:#0e5d7b;width:148px;margin-left:22px}.study-card{position:absolute;left:118px;top:80px;width:205px;height:132px;background:var(--navy);color:#fff;border-radius:14px;padding:20px;box-shadow:var(--shadow);z-index:2}.study-card strong,.study-card span{display:block}.study-card span{font-size:.8rem;color:#dbe7ee}.chart{display:flex;align-items:flex-end;gap:10px;height:45px;margin-top:12px}.chart b{display:block;width:24px;border-bottom:2px solid var(--cyan);height:var(--h,20px);position:relative}.chart b:nth-child(1){--h:22px}.chart b:nth-child(2){--h:35px}.chart b:nth-child(3){--h:28px}.chart b:nth-child(4){--h:42px}.chart b:nth-child(5){--h:48px}.note-card{position:absolute;right:62px;top:80px;width:170px;height:155px;background:#fff;border-radius:16px;box-shadow:var(--shadow);padding:30px 22px}.note-card div{height:7px;border-radius:9px;background:#dfe8ec;margin-bottom:13px}.note-card div:nth-child(2){width:70%}.note-card div:nth-child(3){width:45%;background:#b7eff1}.check{position:absolute;right:-12px;top:58px;background:var(--cyan);color:#fff;width:34px;height:34px;border-radius:50%;display:grid;place-items:center;font-weight:700}.open-book{position:absolute;right:55px;bottom:40px;width:270px;height:115px;background:#fff;border-radius:18px 18px 24px 24px;box-shadow:0 13px 25px rgba(19,30,53,.12);transform:rotate(4deg);display:flex;align-items:center;justify-content:space-evenly;font-family:Alexandria;color:#557}.open-book:before{content:"";position:absolute;left:50%;top:0;bottom:0;border-left:1px solid #dbe3e8}.open-book span{font-size:40px;color:var(--cyan)}.open-book small{font-size:16px}
/* Cards */
.resource-grid{display:grid;grid-template-columns:repeat(4,1fr);gap:14px}.resource-card{min-height:115px;border:1px solid #dfe6eb;border-radius:15px;padding:18px;display:flex;gap:14px;align-items:flex-start;background:#fff;box-shadow:0 6px 18px rgba(19,30,53,.035);transition:.2s}.resource-card:hover,.subject-card:hover,.mini-card:hover{transform:translateY(-2px);border-color:#addfe3;box-shadow:0 10px 22px rgba(19,30,53,.07)}.resource-card .icon{width:48px;height:48px;display:grid;place-items:center;border-radius:50%;background:var(--navy);color:#fff;flex:0 0 auto}.resource-card .icon.accent{background:var(--cyan)}.resource-card strong{display:block;font-size:.92rem}.resource-card small{display:block;color:#6c7586;line-height:1.45;font-size:.72rem;margin-top:5px}.subject-grid{display:grid;grid-template-columns:repeat(5,1fr);gap:16px}.subject-card{min-height:175px;border:1px solid #dce5e9;border-radius:16px;padding:24px 18px;text-align:center;display:flex;flex-direction:column;align-items:center;justify-content:center;background:#fff;position:relative;transition:.2s}.subject-card.featured{background:linear-gradient(180deg,#f2fdfe,#fff)}.subject-icon{width:52px;height:52px;color:var(--navy);display:grid;place-items:center;font-size:1.5rem}.subject-card.featured .subject-icon{color:var(--cyan)}.subject-card strong{margin:8px 0 3px}.subject-card small{font-size:.67rem;color:#778192}.subject-card em{position:absolute;bottom:12px;border:1px solid #9fe6ea;width:27px;height:27px;border-radius:50%;display:grid;place-items:center;color:var(--cyan);font-style:normal}.path-grid{display:grid;grid-template-columns:repeat(5,1fr);gap:14px}.board-grid{display:grid;grid-template-columns:repeat(6,1fr);gap:12px}.mini-card{min-height:118px;border:1px solid #dfe6ea;border-radius:14px;padding:18px 15px;background:#fff;display:grid;grid-template-columns:42px 1fr;grid-template-rows:auto auto;column-gap:10px;transition:.2s}.mini-card>span{grid-row:1/3;width:40px;height:40px;color:var(--navy);display:grid;place-items:center}.mini-card strong{font-size:.76rem;line-height:1.35}.mini-card small{font-size:.64rem;color:#768092;line-height:1.4;margin-top:4px}
/* Chapter */
.chapter-strip{background:var(--navy);border-radius:16px;padding:18px;color:#fff;display:grid;grid-template-columns:1.05fr 1.95fr;gap:20px;align-items:center}.chapter-lead{display:flex;gap:14px;align-items:center}.molecule{width:64px;height:64px;border:1px solid var(--cyan);border-radius:50%;display:grid;place-items:center;color:var(--cyan);font-size:1.4rem}.chapter-lead strong{font-family:Alexandria;display:block}.chapter-lead small{display:block;color:var(--cyan);font-size:.68rem;margin:2px 0}.chapter-lead p{font-size:.68rem;color:#d9e2e8;margin:5px 0 0}.chapter-actions{display:grid;grid-template-columns:repeat(6,1fr);gap:8px}.chapter-actions a{background:#fff;color:var(--navy);border-radius:10px;min-height:66px;padding:8px;display:flex;align-items:center;justify-content:center;gap:5px;text-align:center;font-size:.66rem;font-weight:600}.chapter-actions a.primary{background:var(--cyan);color:#fff}.chapter-actions svg{font-size:1rem;flex:0 0 auto}
/* Challenge */
.split-grid{display:grid;grid-template-columns:1fr 1fr;gap:18px}.panel{border:1px solid #dbe4e9;border-radius:16px;padding:22px;background:#fff}.panel h2{font-family:Alexandria;font-size:1.12rem;margin:0 0 15px}.challenge{display:grid;grid-template-columns:1.5fr .7fr;gap:18px;align-items:center}.challenge>div:first-child{border:1px solid #e2e8ec;border-radius:12px;padding:16px}.challenge strong,.challenge small{display:block}.challenge strong{font-size:.8rem}.challenge small{font-size:.68rem;color:#778192;margin:8px 0 13px}.streak{text-align:center}.streak span,.streak small,.streak strong{display:block}.streak strong{font-family:Alexandria;font-size:1.25rem}.dots{font-size:.72rem;color:var(--cyan);letter-spacing:.15em;margin-top:9px}.trend-list{display:flex;flex-direction:column}.trend-list a{font-size:.73rem;padding:8px 4px;border-bottom:1px solid #edf1f3;display:flex;justify-content:space-between}.trend-list a:hover{color:var(--cyan)}
/* Closing/footer */
.closing{margin-top:25px;background:linear-gradient(90deg,#f1f8fb,#eafafd);padding:34px 0}.closing-inner{display:grid;grid-template-columns:.9fr 1.4fr;align-items:center;gap:30px}.closing h2{font-family:Alexandria;font-size:clamp(1.7rem,3vw,2.7rem);line-height:1.15;margin:0}.closing h2 em{font-style:normal;color:var(--cyan)}.closing p{font-size:.82rem;color:#5f697a}.mountain{height:135px;position:relative;background:linear-gradient(145deg,transparent 35%,#dfeaf3 36% 55%,transparent 56%),linear-gradient(35deg,transparent 42%,#aebfd0 43% 58%,transparent 59%);background-size:220px 120px;background-repeat:no-repeat;background-position:center bottom}.mountain span{position:absolute;left:58%;top:2px;color:var(--cyan);font-size:30px}.tagline{font-size:.73rem;margin-top:8px}.tagline b{color:var(--cyan)}.site-footer{background:var(--navy);color:#fff;padding:38px 0 16px}.footer-grid{display:grid;grid-template-columns:1.3fr repeat(4,1fr);gap:38px}.footer-grid>div{display:flex;flex-direction:column;align-items:flex-start;gap:8px}.footer-grid strong{font-family:Alexandria;font-size:.82rem}.footer-grid a{font-size:.7rem;color:#d5deea}.footer-grid a:hover{color:var(--cyan)}.footer-brand p,.footer-brand small{font-size:.7rem;color:#c7d3df}.footer-bottom{border-top:1px solid rgba(255,255,255,.12);margin-top:26px;padding-top:15px;display:flex;justify-content:space-between;font-size:.63rem;color:#b8c4d0}
/* Content pages */
.page-hero{padding:45px 0 28px;background:linear-gradient(180deg,#f7fbfc,#fff)}.page-hero h1{font-family:Alexandria;font-size:clamp(2rem,4vw,3.5rem);letter-spacing:-.03em;margin:8px 0}.eyebrow{font-size:.72rem;color:var(--cyan);font-weight:700;letter-spacing:.08em;text-transform:uppercase}.page-meta{display:flex;flex-wrap:wrap;gap:8px;margin-top:12px}.page-meta span{font-size:.68rem;background:#eef7f8;padding:6px 9px;border-radius:999px}.content-section{padding:12px 0}.content-width{width:min(900px,calc(100% - 40px));margin:auto}.prose{font-size:.98rem;color:#2f3a51}.prose h2,.prose h3{font-family:Alexandria;color:var(--navy)}.prose p{margin:0 0 1em}.prose ul,.prose ol{padding-left:1.3em}.content-image{margin:12px 0}.content-image img{border-radius:16px;width:100%}.content-image figcaption{font-size:.72rem;color:#6f7888;margin-top:8px}.video-wrap{aspect-ratio:16/9;border-radius:16px;overflow:hidden;background:#000}.video-wrap iframe{width:100%;height:100%;border:0}.math-block{background:#f8fbfc;border:1px solid #dfe9ec;border-radius:12px;padding:18px;overflow:auto}.callout{border-left:4px solid var(--cyan);background:#f2fcfc;padding:18px;border-radius:0 12px 12px 0}.callout p{margin:5px 0 0}.download-card{display:flex;align-items:center;gap:14px;padding:18px;border:1px solid #dbe5e9;border-radius:14px;background:#fff}.download-card>span{width:48px;height:48px;border-radius:50%;background:var(--navy);color:#fff;display:grid;place-items:center}.download-card small{display:block;color:#798292}.pdf-card{border:1px solid #dde5e9;border-radius:16px;overflow:hidden}.pdf-card>div{display:flex;justify-content:space-between;align-items:center;padding:14px}.pdf-card object{width:100%;height:620px;border:0;border-top:1px solid #e6ecef}.question-block{border:1px solid #dbe4e8;border-radius:16px;padding:22px;background:#fff}.question-meta{font-size:.7rem;color:var(--cyan);font-weight:600;text-transform:uppercase}.question-text{margin:10px 0 15px}.options{display:grid;gap:8px}.options div{background:#f7fafb;padding:11px 13px;border-radius:10px}.question-block details{margin-top:14px;border-top:1px solid #e4eaed;padding-top:12px}.question-block summary{font-weight:600;cursor:pointer}.generic-cards{display:grid;grid-template-columns:repeat(3,1fr);gap:14px}.generic-cards a{border:1px solid #dde6ea;border-radius:14px;padding:18px}.generic-cards p{font-size:.78rem;color:#748092}
/* Listing/search */
.listing-hero{padding:42px 0 26px}.listing-hero h1{font-family:Alexandria;font-size:clamp(2rem,4vw,3.4rem);margin:0}.content-grid{display:grid;grid-template-columns:repeat(3,1fr);gap:18px;padding-bottom:48px}.content-card{border:1px solid #dce5e9;border-radius:16px;padding:18px;background:#fff;display:flex;flex-direction:column;min-height:180px}.content-card .badge{font-size:.62rem;color:var(--cyan);font-weight:700;text-transform:uppercase}.content-card h3{font-family:Alexandria;font-size:1rem;margin:8px 0}.content-card p{font-size:.74rem;color:#748092}.content-card .meta{margin-top:auto;font-size:.64rem;color:#8791a2}.empty{padding:45px;text-align:center;border:1px dashed #cbd7dd;border-radius:16px;color:#798394}.filters{display:grid;grid-template-columns:1fr repeat(4,160px) 120px;gap:10px;margin:18px 0 26px}.filters input,.filters select{height:44px;border:1px solid #d5e0e5;border-radius:10px;padding:0 12px;font-family:Poppins;background:#fff}
/* responsive */
@media(max-width:980px){.desktop-nav{display:none}.menu-btn{display:block}.mobile-menu.open{display:flex;flex-direction:column;padding:12px 20px 18px;border-top:1px solid #edf1f3}.mobile-menu a{padding:10px 0}.hero-grid{grid-template-columns:1fr}.hero-art{height:320px}.resource-grid{grid-template-columns:repeat(2,1fr)}.subject-grid{grid-template-columns:repeat(3,1fr)}.path-grid{grid-template-columns:repeat(3,1fr)}.board-grid{grid-template-columns:repeat(3,1fr)}.chapter-strip{grid-template-columns:1fr}.chapter-actions{grid-template-columns:repeat(3,1fr)}.footer-grid{grid-template-columns:repeat(3,1fr)}.footer-brand{grid-column:1/-1}.content-grid{grid-template-columns:repeat(2,1fr)}.filters{grid-template-columns:1fr 1fr 1fr}.filters input{grid-column:1/-1}}
@media(max-width:640px){.container{width:min(100% - 26px,1180px)}.header-inner{height:62px}.brand-logo{gap:7px}.brand-logo .natscix{font-size:24px}.brand-logo .bar{height:19px}.brand-logo .learn{font-size:9px;letter-spacing:.34em}.hide-sm,.header-actions .btn-outline{display:none}.hero{padding-top:28px}.hero h1{font-size:2.65rem}.hero-sub{font-size:.88rem}.hero-art{height:260px}.study-card{left:30px;top:45px;transform:scale(.82);transform-origin:top left}.note-card{right:18px;top:35px;transform:scale(.78);transform-origin:top right}.book-stack{left:20px;bottom:38px;transform:scale(.75) rotate(-4deg);transform-origin:bottom left}.open-book{right:10px;bottom:20px;transform:scale(.72) rotate(4deg);transform-origin:bottom right}.selectors{grid-template-columns:1fr 1fr}.resource-grid,.subject-grid,.path-grid,.board-grid,.split-grid,.content-grid,.generic-cards{grid-template-columns:1fr}.resource-card{min-height:auto}.subject-card{min-height:145px}.chapter-actions{grid-template-columns:1fr 1fr}.challenge{grid-template-columns:1fr}.closing-inner{grid-template-columns:1fr}.mountain{height:90px}.footer-grid{grid-template-columns:1fr 1fr;gap:24px}.footer-brand{grid-column:1/-1}.footer-bottom{flex-direction:column;gap:6px}.filters{grid-template-columns:1fr}.filters input{grid-column:auto}.pdf-card object{height:460px}}
.content-columns{display:grid;grid-template-columns:repeat(var(--cols),1fr);gap:14px}.column-card{border:1px solid #dde6ea;border-radius:14px;padding:16px}.column-card img{border-radius:10px;margin-bottom:12px;aspect-ratio:16/10;object-fit:cover;width:100%}.column-card strong{display:block}.column-card p{font-size:.8rem;color:#6e7889}.column-card a{font-size:.75rem;color:var(--cyan);font-weight:600}.gallery-grid{display:grid;grid-template-columns:repeat(3,1fr);gap:12px}.gallery-grid figure{margin:0;border-radius:13px;overflow:hidden;background:#f6fafb;border:1px solid #e0e8eb}.gallery-grid img{width:100%;aspect-ratio:4/3;object-fit:cover}.gallery-grid figcaption{padding:8px;font-size:.68rem;color:#707a8b}.accordion details{border:1px solid #dce5e9;border-radius:12px;padding:14px 16px;margin-bottom:9px}.accordion summary{font-weight:600;cursor:pointer}.accordion details div{padding-top:8px;font-size:.86rem;color:#596477}.tab-buttons{display:flex;gap:6px;overflow:auto;border-bottom:1px solid #dce5e9}.tab-buttons button{border:0;background:none;padding:10px 13px;font-family:Poppins;font-weight:600;color:#6b7586;cursor:pointer;border-bottom:2px solid transparent}.tab-buttons button.active{color:var(--navy);border-bottom-color:var(--cyan)}.tab-panel{display:none;padding:16px 4px;font-size:.9rem;color:#566174}.tab-panel.active{display:block}.table-scroll{overflow:auto}.content-table{border-collapse:collapse;width:100%;font-size:.82rem}.content-table th,.content-table td{border:1px solid #dce5e9;padding:10px;text-align:left}.content-table th{background:#f4f9fa}.quote-block{margin:0;border-left:4px solid var(--cyan);padding:16px 20px;background:#f5fbfc;border-radius:0 12px 12px 0;font-family:Alexandria;font-size:1.1rem}.quote-block cite{display:block;font-family:Poppins;font-size:.72rem;color:#728092;margin-top:8px}.content-divider{border:0;border-top:1px solid #dce5e9;margin:20px 0}@media(max-width:720px){.content-columns{grid-template-columns:1fr!important}.gallery-grid{grid-template-columns:1fr 1fr}}