:root{--bg: #020817;--surface: #0A1628;--surface-2: #0F1F3D;--surface-3: #142a50;--line: rgba(30, 58, 95, .75);--line-2: #1E3A5F;--fg: #F8FAFC;--fg-2: #CBD5E1;--fg-3: #94A3B8;--accent: #6366F1;--accent-2: #4F46E5;--accent-hi: #A5B4FC;--accent-tint: rgba(99, 102, 241, .12);--accent-ring: rgba(99, 102, 241, .4);--cyan: #06B6D4;--cyan-hi: #67E8F9;--cyan-tint: rgba(6, 182, 212, .1);--amber: #F59E0B;--amber-hi: #FBBF24;--amber-tint: rgba(245, 158, 11, .12);--green: #10B981;--green-hi: #34D399;--green-tint: rgba(16, 185, 129, .12);--rose: #EF4444;--rose-hi: #FB7185;--rose-tint: rgba(239, 68, 68, .12);--code-bg: #040b1c;--f-display: "Space Grotesk", ui-sans-serif, system-ui, sans-serif;--f-body: "Inter", ui-sans-serif, system-ui, -apple-system, "Segoe UI", sans-serif;--f-mono: "JetBrains Mono", ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;--r-md: 14px;--r-lg: 18px;--r-xl: 22px;--nav-h: 56px;--sub-h: 48px}@media(min-width:768px){:root{--nav-h: 64px}}body{background:var(--bg);color:var(--fg-2);font-family:var(--f-body);overflow-x:hidden}#learn-root{min-height:100vh}.learn-main,.learn-static{padding-top:var(--nav-h)}.learn-main h1,.learn-main h2,.learn-main h3,.learn-main h4,.learn-static h1,.learn-static h2,.learn-static h3,.learn-static h4{font-family:var(--f-display);color:var(--fg);margin:0;letter-spacing:-.01em;text-wrap:balance}.learn-main p,.learn-static p{margin:0}.learn-main a,.learn-static a{color:inherit;text-decoration:none}.ic{width:20px;height:20px;flex:none;display:inline-block;vertical-align:middle}.wrap{max-width:1200px;margin:0 auto;padding-left:16px;padding-right:16px}@media(min-width:768px){.wrap{padding-left:24px;padding-right:24px}}.wrap.narrow{max-width:760px}.muted{color:var(--fg-3);font-size:.82rem}.learn-subnav{position:sticky;top:var(--nav-h);z-index:40;background:#020817eb;backdrop-filter:blur(16px);-webkit-backdrop-filter:blur(16px);border-bottom:1px solid var(--line)}.learn-subnav-inner{display:flex;align-items:center;gap:12px;height:var(--sub-h)}.learn-tabs{display:flex;gap:4px;overflow-x:auto;scrollbar-width:none;flex:1;min-width:0}.learn-tabs::-webkit-scrollbar{display:none}.learn-tabs a{white-space:nowrap;padding:7px 12px;border-radius:999px;font-size:.86rem;font-weight:500;color:var(--fg-3)}.learn-tabs a:hover{color:var(--fg);background:#6366f114}.learn-tabs a[aria-current=page]{color:var(--fg);background:var(--accent-tint);box-shadow:inset 0 0 0 1px var(--accent-ring)}.search-trigger{display:inline-flex;align-items:center;gap:8px;height:34px;padding:0 12px;border-radius:999px;border:1px solid var(--line-2);background:var(--surface);color:var(--fg-3);font-size:.86rem;cursor:pointer;flex:none}.search-trigger:hover{border-color:var(--accent-ring);color:var(--fg)}.search-trigger .ic{width:16px;height:16px}.kbd{font:500 .72rem/1 var(--f-mono);padding:3px 6px;border-radius:6px;border:1px solid var(--line-2)}@media(max-width:640px){.search-trigger span{display:none}.search-trigger{width:34px;padding:0;justify-content:center}}.eyebrow{display:inline-flex;align-items:center;gap:8px;padding:7px 14px;border-radius:999px;border:1px solid var(--accent-ring);background:var(--accent-tint);color:var(--accent-hi);font:600 .74rem/1 var(--f-display);letter-spacing:.14em;text-transform:uppercase;justify-self:start}.eyebrow .ic{width:15px;height:15px}.eyebrow.amber{color:var(--amber-hi);border-color:#f59e0b66;background:var(--amber-tint)}.eyebrow.green{color:var(--green-hi);border-color:#10b98166;background:var(--green-tint)}.hl{color:#818cf8}.tile{width:48px;height:48px;border-radius:14px;display:grid;place-items:center;flex:none;color:var(--accent-hi);background:var(--accent-tint);border:1px solid var(--accent-ring)}.tile .ic{width:22px;height:22px}.tile-lg{width:64px;height:64px;border-radius:18px}.tile-lg .ic{width:28px;height:28px}.tile-indigo{color:var(--accent-hi);background:var(--accent-tint);border-color:var(--accent-ring)}.tile-amber{color:var(--amber-hi);background:var(--amber-tint);border-color:#f59e0b61}.tile-green{color:var(--green-hi);background:var(--green-tint);border-color:#10b98161}.tile-cyan{color:var(--cyan-hi);background:var(--cyan-tint);border-color:#06b6d457}.tile-rose{color:var(--rose-hi);background:var(--rose-tint);border-color:#ef44445c}.badge{display:inline-flex;align-items:center;gap:6px;padding:6px 12px;border-radius:999px;font:600 .7rem/1 var(--f-display);letter-spacing:.1em;text-transform:uppercase;color:var(--accent-hi);background:var(--accent-tint);border:1px solid var(--accent-ring);white-space:nowrap}.badge.amber{color:var(--amber-hi);background:var(--amber-tint);border-color:#f59e0b66}.badge.green{color:var(--green-hi);background:var(--green-tint);border-color:#10b98166}.badge.rose{color:var(--rose-hi);background:var(--rose-tint);border-color:#ef444466}.badge.small{padding:5px 9px;font-size:.64rem}.card{position:relative;background:var(--surface-2);border:1px solid var(--line-2);border-radius:var(--r-xl)}a.card{transition:border-color .15s,transform .15s}a.card:hover{border-color:var(--accent-ring);transform:translateY(-2px)}.btn{display:inline-flex;align-items:center;justify-content:center;gap:8px;min-height:44px;padding:0 20px;border-radius:12px;font-weight:600;border:1px solid transparent;cursor:pointer}.learn-main .btn-primary,.learn-main .btn-secondary,.learn-static .btn-primary,.learn-static .btn-secondary{display:inline-flex;align-items:center;justify-content:center;gap:8px}.learn-main .btn-primary .ic,.learn-main .btn-secondary .ic,.learn-static .btn-primary .ic,.learn-static .btn-secondary .ic{width:18px;height:18px}.chip{display:inline-flex;align-items:center;gap:6px;min-height:34px;padding:0 13px;border-radius:999px;border:1px solid var(--line-2);background:var(--surface);color:var(--fg-2);font:500 .86rem/1 var(--f-body);white-space:nowrap;cursor:pointer}.chip:hover{border-color:var(--accent-ring);color:var(--fg)}.chip[aria-pressed=true]{background:var(--accent-2);border-color:var(--accent-2);color:#fff}.chip .count{font-size:.74rem;opacity:.7}.chip:disabled{opacity:.35;cursor:default}.chip-row{display:flex;gap:8px;flex-wrap:wrap}.chip-scroll{display:flex;gap:8px;overflow-x:auto;padding-bottom:4px;scrollbar-width:none}.chip-scroll::-webkit-scrollbar{display:none}.meta{display:flex;flex-wrap:wrap;align-items:center;gap:6px 16px;color:var(--fg-3);font-size:.86rem}.meta span{display:inline-flex;align-items:center;gap:6px}.meta .ic{width:15px;height:15px;color:var(--accent-hi)}.crumbs{display:flex;flex-wrap:wrap;align-items:center;gap:6px;font-size:.84rem;color:var(--fg-3)}.crumbs a:hover{color:var(--accent-hi)}.crumbs a{display:inline-block;padding:7px 0}.crumbs .ic{width:13px;height:13px;opacity:.6}.field{display:flex;align-items:center;gap:10px;min-height:46px;padding:0 14px;border-radius:12px;border:1px solid var(--line-2);background:var(--surface)}.field:focus-within{border-color:var(--accent);box-shadow:0 0 0 3px #6366f12e}.field .ic{color:var(--fg-3)}.field input{flex:1;min-width:0;background:transparent;border:0;outline:none;color:var(--fg);font-size:1rem}.bar{height:7px;border-radius:999px;background:#6366f124;overflow:hidden}.bar>i{display:block;height:100%;border-radius:inherit;background:linear-gradient(90deg,var(--accent),var(--cyan));width:var(--w, 0%);transition:width .4s ease}.icon-btn{width:40px;height:40px;border-radius:12px;display:grid;place-items:center;color:var(--fg-3);background:transparent;border:0;cursor:pointer}.icon-btn:hover{color:var(--fg);background:#6366f11a}.page-hero{padding-block:clamp(28px,6vw,56px) 8px}.page-hero .wrap{display:grid;gap:16px}.page-title{font-size:clamp(1.9rem,6vw,2.9rem);line-height:1.1;font-weight:700}.lead-text{font-size:clamp(1rem,2.4vw,1.12rem);line-height:1.7;color:var(--fg-3);max-width:66ch}.lead-text a{color:var(--accent-hi);text-decoration:underline}.hub-hero .wrap{justify-items:center;text-align:center}.hub-title{font-size:clamp(2.1rem,7vw,3.6rem);line-height:1.08;font-weight:700;max-width:18ch}.hub-hero .lead-text{margin:0 auto}.stats{display:flex;flex-wrap:wrap;justify-content:center;gap:10px;margin-top:8px}.stat{padding:12px 18px;border-radius:16px;border:1px solid var(--line-2);background:var(--surface);display:grid;gap:2px;min-width:120px}.stat b{font:700 1.6rem/1 var(--f-display);color:var(--fg)}.stat span{font-size:.8rem;color:var(--fg-3)}.section-sm{padding-top:clamp(28px,5vw,48px)}.subhead{display:flex;align-items:flex-end;justify-content:space-between;gap:12px;flex-wrap:wrap;margin:0 0 16px}.subhead h2{font-size:clamp(1.35rem,4vw,1.8rem)}.subhead p{color:var(--fg-3);font-size:.94rem;margin-top:6px}.book-grid{display:grid;gap:16px;grid-template-columns:repeat(auto-fit,minmax(min(100%,340px),1fr))}.book-card{padding:22px;display:grid;gap:12px;align-content:start}.book-card-top{display:flex;align-items:center;justify-content:space-between}.book-card h2{font-size:1.5rem}.book-card p{color:var(--fg-3);line-height:1.6}.book-card .go,.extra .go{display:inline-flex;align-items:center;gap:8px;color:var(--accent-hi);font-weight:600;font-size:.9rem}.book-card .go .ic,.extra .go .ic{width:16px;height:16px}.extras-grid{display:grid;gap:14px;grid-template-columns:repeat(auto-fit,minmax(min(100%,260px),1fr))}.extra{padding:20px;display:grid;gap:10px;align-content:start}.extra h3{font-size:1.15rem}.extra p{color:var(--fg-3);font-size:.92rem;line-height:1.55}.steps{list-style:none;margin:0;padding:0;display:grid;gap:14px;grid-template-columns:repeat(auto-fit,minmax(min(100%,260px),1fr))}.step{padding:20px;display:grid;gap:10px;align-content:start}.step b{color:var(--fg);font:600 1.1rem/1.3 var(--f-display)}.step span:not(.tile){color:var(--fg-3);font-size:.92rem;line-height:1.55}.faq{display:grid;gap:10px}.faq-item{padding:0;border-radius:var(--r-lg)}.faq-item summary{list-style:none;cursor:pointer;display:flex;justify-content:space-between;align-items:center;gap:12px;padding:16px 18px;color:var(--fg);font:600 1rem/1.35 var(--f-display)}.faq-item summary::-webkit-details-marker{display:none}.faq-item summary .ic{color:var(--fg-3);transition:transform .2s}.faq-item[open] summary .ic{transform:rotate(180deg)}.faq-item p{padding:0 18px 16px;color:var(--fg-3);line-height:1.65}.cta-strip{padding:22px;display:flex;gap:16px;align-items:center;justify-content:space-between;flex-wrap:wrap}.cta-strip>div:first-child{display:grid;gap:4px}.cta-strip b{color:var(--fg);font:600 1.2rem/1.3 var(--f-display)}.cta-strip span{color:var(--fg-3)}.book-head{display:flex;gap:18px;align-items:flex-start}.book-head>div{display:grid;gap:12px;min-width:0}.book-head .badge{justify-self:start}@media(max-width:560px){.book-head{flex-direction:column}}.progress-row{display:grid;gap:6px;max-width:420px}.progress-row small{color:var(--fg-3);font-size:.82rem}.lock-actions{display:flex;gap:10px;flex-wrap:wrap;align-items:center}.part-block{margin-top:36px}.part-block:first-child{margin-top:0}.part-head{display:flex;align-items:center;gap:14px;margin-bottom:14px}.part-head h2{font-size:1.3rem}.part-head p{color:var(--fg-3);font-size:.9rem;margin-top:4px}.ch-grid{display:grid;gap:12px;grid-template-columns:repeat(auto-fill,minmax(min(100%,300px),1fr))}.ch-card{padding:18px;display:grid;gap:8px;align-content:start;border-radius:var(--r-lg)}.ch-card-top{display:flex;justify-content:space-between;align-items:center}.ch-num{font:600 .78rem/1 var(--f-mono);color:var(--accent-hi)}.ch-card h3{font-size:1.08rem;line-height:1.3}.ch-card p{color:var(--fg-3);font-size:.88rem;line-height:1.55;display:-webkit-box;-webkit-line-clamp:3;-webkit-box-orient:vertical;overflow:hidden}.ch-card .done{color:var(--green-hi)}.lock-badge{display:inline-flex;align-items:center;gap:5px;font-size:.72rem;font-weight:600;color:var(--fg-3);padding:4px 8px;border-radius:999px;border:1px solid var(--line-2)}.lock-badge .ic{width:13px;height:13px}.starter-grid{display:grid;gap:12px;grid-template-columns:repeat(auto-fill,minmax(min(100%,210px),1fr))}.starter{padding:18px;display:grid;gap:8px;align-content:start;border-radius:var(--r-lg)}.starter .badge{justify-self:start}.starter b{color:var(--fg);font:600 1.02rem/1.3 var(--f-display)}.starter span:not(.badge){color:var(--fg-3);font-size:.85rem;line-height:1.5}.lock-card{padding:clamp(20px,4vw,28px);display:grid;gap:12px;justify-items:start;margin-top:24px;border-color:var(--accent-ring);background:linear-gradient(180deg,#4f46e524,#0f1f3df2)}.lock-card h2{font-size:clamp(1.2rem,3.6vw,1.5rem)}.lock-sub{color:var(--fg-2);line-height:1.6;max-width:60ch}.locked-meta{color:var(--amber-hi)}.preview-chips{margin-top:4px}.calc-preview{list-style:none;margin:0;padding:0;display:grid;gap:10px;grid-template-columns:repeat(auto-fill,minmax(min(100%,300px),1fr))}.calc-preview li{padding:14px;display:flex;gap:12px;align-items:center;border-radius:var(--r-lg)}.calc-preview li div{display:grid;gap:2px}.calc-preview b{color:var(--fg)}.calc-preview span:not(.tile){color:var(--fg-3);font-size:.86rem}.read-progress{position:fixed;top:var(--nav-h);left:0;right:0;height:3px;z-index:55;transform-origin:0 50%;background:linear-gradient(90deg,var(--accent),var(--cyan))}.reader{max-width:1320px;margin:0 auto;padding:clamp(20px,4vw,36px) 16px 40px;display:grid;grid-template-columns:minmax(0,1fr);gap:40px}@media(min-width:1100px){.reader{grid-template-columns:260px minmax(0,1fr);gap:44px;padding-inline:24px}}@media(min-width:1380px){.reader{grid-template-columns:260px minmax(0,1fr) 210px}}.book-nav,.toc-rail{display:none}@media(min-width:1100px){.book-nav{display:block;position:sticky;top:calc(var(--nav-h) + var(--sub-h) + 16px);align-self:start;max-height:calc(100vh - var(--nav-h) - var(--sub-h) - 32px);overflow-y:auto;padding-right:6px;scrollbar-width:thin;scrollbar-color:var(--line-2) transparent}}@media(min-width:1380px){.toc-rail{display:block;position:sticky;top:calc(var(--nav-h) + var(--sub-h) + 16px);align-self:start;max-height:calc(100vh - var(--nav-h) - var(--sub-h) - 32px);overflow-y:auto}.otp-inline{display:none}}.nav-book{display:grid;gap:10px;padding:14px;border:1px solid var(--line-2);border-radius:var(--r-lg);background:var(--surface);margin-bottom:14px}.nav-book a.title{display:flex;align-items:center;gap:12px;color:var(--fg);font:600 1rem/1.25 var(--f-display)}.nav-book .tile{width:38px;height:38px;border-radius:11px}.nav-book .tile .ic{width:18px;height:18px}.nav-book .bar{height:6px}.nav-book small{color:var(--fg-3);font-size:.78rem}.nav-group{margin-top:12px}.nav-group-title{padding:0 10px 6px;color:var(--fg-3);font:600 .66rem/1.3 var(--f-display);letter-spacing:.13em;text-transform:uppercase}.nav-list{list-style:none;margin:0;padding:0;display:grid;gap:2px}.nav-list a{display:flex;align-items:flex-start;gap:10px;padding:7px 10px;border-radius:10px;color:var(--fg-2);font-size:.88rem;line-height:1.35}.nav-list a:hover{background:#6366f114;color:var(--fg)}.nav-list a[aria-current=page]{background:var(--accent-tint);color:var(--fg);box-shadow:inset 0 0 0 1px var(--accent-ring)}.nav-list .n{min-width:22px;color:var(--fg-3);font:500 .76rem/1.6 var(--f-mono)}.nav-list a[aria-current=page] .n{color:var(--accent-hi)}.nav-list .done{margin-left:auto;color:var(--green-hi)}.nav-list .done .ic{width:15px;height:15px}.article{min-width:0;max-width:780px;width:100%;justify-self:center}.ch-head{display:grid;gap:14px;padding-bottom:24px;margin-bottom:28px;border-bottom:1px solid var(--line)}.ch-head h1{font-size:clamp(1.9rem,6.4vw,2.9rem);line-height:1.1;font-weight:700;letter-spacing:-.02em}.ch-head .row{display:flex;align-items:center;justify-content:space-between;gap:12px;flex-wrap:wrap}.size-toggle{display:inline-flex;border:1px solid var(--line-2);border-radius:999px;overflow:hidden}.size-toggle button{min-width:40px;height:34px;color:var(--fg-3);font-weight:600;background:transparent;border:0;cursor:pointer}.size-toggle button[aria-pressed=true]{background:var(--accent-tint);color:var(--fg)}.otp-inline{margin-bottom:24px;border:1px solid var(--line-2);border-radius:var(--r-md);background:var(--surface)}.otp-inline summary{list-style:none;cursor:pointer;display:flex;align-items:center;justify-content:space-between;gap:12px;padding:13px 16px;color:var(--fg);font:600 .94rem/1 var(--f-display)}.otp-inline summary::-webkit-details-marker{display:none}.otp-inline summary .ic{color:var(--fg-3);transition:transform .2s}.otp-inline[open] summary .ic{transform:rotate(180deg)}.otp-inline ol{margin:0;padding:0 16px 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4px;color:var(--fg-3);font-size:.82rem;white-space:nowrap}.calc-out{padding:14px;border-radius:14px;border:1px solid var(--accent-ring);background:linear-gradient(180deg,#4f46e524,#4f46e50d);display:grid;gap:10px}.calc-main{display:flex;align-items:baseline;gap:10px;flex-wrap:wrap}.calc-main small{color:var(--fg-3);font:600 .7rem/1 var(--f-display);letter-spacing:.12em;text-transform:uppercase;width:100%}.calc-main b{font:700 2rem/1 var(--f-display);color:var(--fg);font-variant-numeric:tabular-nums}.calc-main span{color:var(--accent-hi);font-weight:600}.calc-extra{display:grid;gap:6px}.calc-extra div{display:flex;justify-content:space-between;gap:12px;font-size:.88rem;color:var(--fg-3)}.calc-extra div b{color:var(--fg);font-weight:600;text-align:right}.calc-note{font-size:.82rem;color:var(--fg-3);line-height:1.5;display:flex;gap:8px}.calc-note .ic{width:16px;height:16px;color:var(--amber-hi);margin-top:1px}.calc-note.warn{color:var(--amber-hi)}.calc-formula{font:500 .82rem/1.5 var(--f-mono);color:var(--fg-3);padding-top:6px;border-top:1px dashed var(--line-2)}.calc-src{font-size:.82rem;color:var(--accent-hi);display:inline-flex;align-items:center;gap:6px}.calc-src .ic{width:15px;height:15px}.site-footer{margin-top:clamp(56px,9vw,100px);border-top:1px solid var(--line-2);background:var(--surface);padding-block:40px}.footer-inner{display:grid;gap:28px}@media(min-width:820px){.footer-inner{grid-template-columns:1.4fr 1fr 1fr}}.site-footer .brand{display:inline-flex;align-items:center;gap:10px;color:var(--fg);font:700 1.2rem/1 var(--f-display);text-decoration:none}.site-footer .brand img{width:32px;height:32px;border-radius:8px}.site-footer .brand em{font-style:normal;color:var(--accent)}.footer-inner p{color:var(--fg-3);line-height:1.7;font-size:.9rem;max-width:44ch;margin-top:12px}.footer-col h4{font:600 .72rem/1 var(--f-display);letter-spacing:.14em;text-transform:uppercase;color:var(--fg-3);margin-bottom:12px}.footer-col ul{list-style:none;margin:0;padding:0;display:grid;gap:9px}.footer-col a{color:var(--fg-2);font-size:.93rem;text-decoration:none}.footer-col a:hover{color:var(--accent-hi)}.footer-base{margin-top:28px;padding-top:18px;border-top:1px solid var(--line-2);display:flex;justify-content:space-between;gap:12px;flex-wrap:wrap;color:var(--fg-3);font-size:.82rem}.toast{position:fixed;left:50%;bottom:calc(24px + env(safe-area-inset-bottom,0px));transform:translate(-50%);z-index:80;display:inline-flex;align-items:center;gap:10px;padding:11px 18px;border-radius:999px;background:var(--surface-3);border:1px solid var(--line-2);color:var(--fg);font-weight:500;box-shadow:0 20px 40px -20px #000c;width:max-content;max-width:calc(100vw - 32px)}.toast .ic{color:var(--green-hi)}body.has-reader-bar .toast{bottom:calc(90px + env(safe-area-inset-bottom,0px))}@media(min-width:1100px){body.has-reader-bar .toast{bottom:24px}}.static-nav{position:fixed;top:0;left:0;right:0;z-index:50;height:var(--nav-h);display:flex;align-items:center;justify-content:space-between;padding:0 16px;background:#0a1628e6;border-bottom:1px solid rgba(30,58,95,.5);-webkit-backdrop-filter:blur(24px);backdrop-filter:blur(24px)}.static-nav .brand{display:inline-flex;align-items:center;gap:10px;color:var(--fg);font:700 1.15rem/1 var(--f-display)}.static-nav .brand img{width:32px;height:32px;border-radius:8px}.static-nav .brand em{font-style:normal;color:#818cf8}.static-nav nav{display:flex;gap:18px;font-size:.92rem;color:var(--fg-3)}@media(max-width:640px){.static-nav nav a:not(:last-child){display:none}}@media(prefers-reduced-motion:reduce){.bar>i,a.card,.prose-skeleton i{transition:none;animation:none}}