@font-face{font-family:"Source Serif 4 Variable";font-style:normal;font-display:swap;font-weight:200 900;src:url(/learn/_next/static/media/source-serif-4-cyrillic-ext-wght-normal.aff33289.woff2) format("woff2-variations");unicode-range:u+0460-052f,u+1c80-1c8a,u+20b4,u+2de0-2dff,u+a640-a69f,u+fe2e-fe2f}@font-face{font-family:"Source Serif 4 Variable";font-style:normal;font-display:swap;font-weight:200 900;src:url(/learn/_next/static/media/source-serif-4-cyrillic-wght-normal.5fc8b187.woff2) format("woff2-variations");unicode-range:u+0301,u+0400-045f,u+0490-0491,u+04b0-04b1,u+2116}@font-face{font-family:"Source Serif 4 Variable";font-style:normal;font-display:swap;font-weight:200 900;src:url(/learn/_next/static/media/source-serif-4-greek-wght-normal.b85e4c85.woff2) format("woff2-variations");unicode-range:u+0370-0377,u+037a-037f,u+0384-038a,u+038c,u+038e-03a1,u+03a3-03ff}@font-face{font-family:"Source Serif 4 Variable";font-style:normal;font-display:swap;font-weight:200 900;src:url(/learn/_next/static/media/source-serif-4-vietnamese-wght-normal.326736c9.woff2) format("woff2-variations");unicode-range:u+0102-0103,u+0110-0111,u+0128-0129,u+0168-0169,u+01a0-01a1,u+01af-01b0,u+0300-0301,u+0303-0304,u+0308-0309,u+0323,u+0329,u+1ea0-1ef9,u+20ab}@font-face{font-family:"Source Serif 4 Variable";font-style:normal;font-display:swap;font-weight:200 900;src:url(/learn/_next/static/media/source-serif-4-latin-ext-wght-normal.ea80ea3f.woff2) format("woff2-variations");unicode-range:u+0100-02ba,u+02bd-02c5,u+02c7-02cc,u+02ce-02d7,u+02dd-02ff,u+0304,u+0308,u+0329,u+1d00-1dbf,u+1e00-1e9f,u+1ef2-1eff,u+2020,u+20a0-20ab,u+20ad-20c4,u+2113,u+2c60-2c7f,u+a720-a7ff}@font-face{font-family:"Source Serif 4 Variable";font-style:normal;font-display:swap;font-weight:200 900;src:url(/learn/_next/static/media/source-serif-4-latin-wght-normal.251dbc47.woff2) format("woff2-variations");unicode-range:u+00??,u+0131,u+0152-0153,u+02bb-02bc,u+02c6,u+02da,u+02dc,u+0304,u+0308,u+0329,u+2000-206f,u+20ac,u+2122,u+2191,u+2193,u+2212,u+2215,u+feff,u+fffd}:root{--paper:#f3f6fa;--paper-2:#e6edf4;--white:#fbfdff;--line:#c5d2e0;--line-soft:#dde6ef;--ink:#061b33;--ink-soft:#46596f;--cyan:#00b5ff;--cyan-light:#29d4ff;--blue:#0089c4;--blue-deep:#006b99;--teal:#0c8f7e;--teal-text:#0a6f62;--amber:#f2b01e;--bad:#b3261e;--font-ui:system-ui,-apple-system,"Segoe UI",Roboto,Helvetica,Arial,sans-serif;--font-read:"Source Serif 4 Variable",Georgia,"Times New Roman",serif;--radius:6px;--measure:66ch}*,:after,:before{box-sizing:border-box}html{-webkit-text-size-adjust:100%}body{margin:0;background:var(--paper);color:var(--ink);font-family:var(--font-ui);font-size:17px;line-height:1.55;font-optical-sizing:auto;-webkit-font-smoothing:antialiased}h1,h2,h3,h4{margin:0;font-weight:700;line-height:1.1;letter-spacing:-.015em}h1{font-size:clamp(2.3rem,5.4vw,3.8rem);letter-spacing:-.025em;line-height:1.03}h2{font-size:clamp(1.55rem,3vw,2.15rem)}h3{font-size:1.22rem;line-height:1.2}p{margin:0}a{color:var(--blue-deep);text-decoration-thickness:1px;text-underline-offset:3px}a:hover{color:var(--ink)}:focus-visible{outline:3px solid var(--blue);outline-offset:3px;border-radius:3px}.skip{position:absolute;left:-999px;top:8px;background:var(--ink);color:#fff;padding:10px 14px;border-radius:var(--radius);z-index:10}.skip:focus{left:8px}.wrap{max-width:1180px;margin:0 auto;padding:0 24px}.soft{color:var(--ink-soft)}.site-header{background:var(--ink);border-bottom:1px solid rgba(0,181,255,.18);color:#fff}.band-dark :focus-visible,.hero :focus-visible,.site-footer :focus-visible,.site-header :focus-visible,.tryit :focus-visible{outline-color:#fff}.bar{display:flex;justify-content:space-between;flex-wrap:wrap;gap:10px 28px;padding-top:14px;padding-bottom:14px}.bar,.brand{align-items:center}.brand{display:inline-flex;gap:10px;text-decoration:none}.brand,.brand:hover{color:#fff}.brand img{display:block;height:26px;width:auto}.brand-sub{font-weight:400;font-size:1.15rem;color:#9fb2c8}.nav{display:flex;align-items:center;flex-wrap:wrap;gap:8px 22px}.nav a:not(.btn){color:#e8eef5;text-decoration:none;font-weight:560}.nav a:not(.btn):hover{text-decoration:underline;text-underline-offset:5px}.site-footer{margin-top:96px;background:var(--ink);padding:36px 0 48px;color:#b9c6d6;font-size:.95rem}main:has(>.band-dark:last-child)+.site-footer{margin-top:0;border-top:1px solid rgba(0,181,255,.18)}.foot{justify-content:space-between;gap:16px 40px}.foot,.foot ul{display:flex;flex-wrap:wrap}.foot ul{gap:8px 24px;list-style:none;margin:0;padding:0}.foot a{color:#fff}.btn{display:inline-flex;align-items:center;justify-content:center;min-height:46px;padding:10px 22px;border:1.5px solid var(--cyan);border-radius:var(--radius);background:var(--cyan);font:600 1rem/1.2 var(--font-ui);text-decoration:none;text-align:center;cursor:pointer}.btn,.btn:hover{color:var(--ink)}.btn:hover{background:var(--cyan-light);border-color:var(--cyan-light)}.btn-ghost{background:transparent}.btn-ghost,.btn-ghost:hover{border-color:var(--ink);color:var(--ink)}.btn-ghost:hover{background:var(--paper-2)}.btn-small{min-height:40px;padding:8px 16px;font-size:.95rem}.btn-light{background:#fff;border-color:#fff;color:var(--ink)}.btn-light:hover{background:var(--paper-2);border-color:var(--paper-2);color:var(--ink)}.btn-outline-light{background:transparent;border-color:#fff;color:#fff}.btn-outline-light:hover{background:rgba(255,255,255,.12);border-color:#fff;color:#fff}.btn-row{display:flex;flex-wrap:wrap;gap:12px}.hero{padding:56px 0 64px;background:var(--ink) url(/learn/contours.svg) center /cover no-repeat;color:#fff}.hero-grid{display:grid;grid-template-columns:minmax(0,.86fr) minmax(0,1.14fr);grid-gap:56px;gap:56px;align-items:center}.hero-copy .lede{margin-top:22px;max-width:34rem;font-size:1.2rem;line-height:1.5;color:#d9e2ec}.hero .btn-ghost{border-color:#5a7696;color:#fff}.hero .btn-ghost:hover{background:rgba(255,255,255,.1);border-color:#fff;color:#fff}.hero-copy .btn-row{margin-top:30px}.byline{margin-top:26px;font-size:.95rem;color:#9fb2c8}.plot{color:var(--ink);background:var(--white);border:1px solid var(--line);border-radius:var(--radius);padding:14px 14px 18px}.plot svg{display:block;width:100%;height:auto}.plot text{font-family:var(--font-ui);fill:var(--ink-soft)}.plot .axis-title{font-size:17px;font-weight:560;fill:var(--ink)}.plot .tick{font-size:15px}.plot .curve-label{font-size:18px;font-weight:700}.plot .band{fill:var(--blue);opacity:0;transition:opacity .18s ease;cursor:pointer}.plot .band.on{opacity:.1}.plot .draw{stroke-dasharray:1;stroke-dashoffset:1;animation:draw 1.7s cubic-bezier(.3,.1,.2,1) .2s forwards}.plot .draw.second{animation-delay:.7s}.plot .dots{opacity:0;animation:fade .6s ease 1.9s forwards}@keyframes draw{to{stroke-dashoffset:0}}@keyframes fade{to{opacity:1}}@media (prefers-reduced-motion:reduce){.plot .draw{animation:none;stroke-dashoffset:0}.plot .dots{animation:none;opacity:1}}.regimes{display:flex;flex-wrap:wrap;gap:8px;margin-top:12px}.regime{min-height:40px;padding:6px 14px;border:1.5px solid var(--line);border-radius:999px;background:transparent;color:var(--ink);font:600 .92rem/1.2 var(--font-ui);cursor:pointer}.regime:hover{border-color:var(--ink)}.regime[aria-pressed=true]{background:var(--ink);border-color:var(--ink);color:#fff}.regime-text{margin-top:14px;min-height:7.4em;font-size:.98rem}.regime-text h3{font-size:1.1rem;margin-bottom:6px}.regime-text p+p{margin-top:6px}.fig-note{margin-top:10px;font-size:.85rem;color:var(--ink-soft)}.fig{background:var(--white);border:1px solid var(--line);border-radius:var(--radius);padding:14px}.fig svg{display:block;width:100%;height:auto}.fig text{font-family:var(--font-ui);fill:var(--ink-soft)}.fig-scroll{overflow-x:auto}.field .check{font-weight:500}.section{padding-top:72px}.section-head{display:flex;flex-wrap:wrap;align-items:baseline;justify-content:space-between;gap:8px 32px;margin-bottom:28px}.section-head p{max-width:32rem;color:var(--ink-soft)}.rows{border-top:2px solid var(--ink)}.row{display:grid;grid-template-columns:minmax(0,1fr) 260px;grid-gap:10px 40px;gap:10px 40px;padding:26px 0;border-bottom:1px solid var(--line)}.row h3{font-size:1.45rem}.row h3 a{color:var(--ink);text-decoration:none}.row h3 a:hover{color:var(--blue-deep);text-decoration:underline;text-underline-offset:5px}.row .summary{margin-top:8px;max-width:40rem;color:var(--ink-soft)}.row .gets{font-size:.95rem;color:var(--ink-soft)}.row .gets strong{display:block;color:var(--ink);font-weight:650;margin-bottom:2px}.meta{display:flex;flex-wrap:wrap;gap:4px 22px;margin:12px 0 0;font-size:.92rem}.meta div{display:flex;gap:6px}.meta dt{color:var(--ink-soft)}.meta dd{margin:0;font-weight:600}.done-mark{display:inline-block;margin-left:4px;padding:2px 10px;border-radius:999px;background:#dff1ed;color:var(--teal-text);font-size:.85rem;font-weight:650}.gives{display:grid;grid-template-columns:repeat(4,minmax(0,1fr));grid-gap:32px;gap:32px;border-top:2px solid var(--ink);padding-top:24px}.gives h3{margin-bottom:8px}.gives p{color:var(--ink-soft);font-size:.97rem}.band-dark{margin-top:96px;border-top:1px solid rgba(0,181,255,.18);background:var(--ink);color:#fff;padding:64px 0}.band-dark p{color:#cfd9e3}.band-grid{display:grid;grid-template-columns:minmax(0,1fr) minmax(0,1.1fr);grid-gap:56px;gap:56px;align-items:start}.band-dark .btn-row{margin-top:28px}.tool-list{list-style:none;margin:0;padding:0;border-top:1px solid #36485c}.tool-list li{padding:18px 0;border-bottom:1px solid #36485c}.tool-list strong{display:block;font-size:1.2rem;font-weight:700}.tool-list span{color:#cfd9e3}.page-head{padding:56px 0 8px}.page-head p{margin-top:16px;max-width:38rem;font-size:1.15rem;color:var(--ink-soft)}.group+.group{margin-top:56px}.group>h2{margin-bottom:18px}.upcoming{list-style:none;margin:0;padding:0;border-top:2px solid var(--ink)}.upcoming li{display:flex;flex-wrap:wrap;align-items:center;justify-content:space-between;gap:8px 24px;padding:16px 0;border-bottom:1px solid var(--line)}.crumb{padding-top:28px;font-size:.95rem}.lesson-head{padding:20px 0 36px;border-bottom:1px solid var(--line)}.lesson-head h1{max-width:24ch}.lesson-head .lede{margin-top:18px;max-width:40rem;font-size:1.2rem;color:var(--ink-soft)}.lesson-grid{display:grid;grid-template-columns:190px minmax(0,1fr);grid-gap:64px;gap:64px;padding-top:40px}.outline{position:-webkit-sticky;position:sticky;top:24px;align-self:start;font-size:.95rem}.outline p{font-weight:650;margin-bottom:8px}.outline ul{list-style:none;margin:0 0 20px;padding:0;border-left:2px solid var(--line)}.outline li a{display:block;padding:5px 0 5px 14px;color:var(--ink-soft);text-decoration:none}.outline li a:hover{color:var(--ink)}.lesson-main{max-width:760px}.lesson-main>section+section{margin-top:64px}.lesson-main>section>h2{margin-bottom:20px;scroll-margin-top:20px}.steps{list-style:none;margin:0;padding:0;counter-reset:step}.steps li{position:relative;counter-increment:step;padding:0 0 34px 64px}.steps li:before{content:counter(step);position:absolute;left:0;top:-2px;width:42px;height:42px;border-radius:50%;background:var(--ink);color:#fff;display:grid;place-items:center;font-weight:700}.steps li:after{content:"";position:absolute;left:20px;top:46px;bottom:4px;width:2px;background:var(--line)}.steps li:last-child{padding-bottom:0}.steps li:last-child:after{display:none}.io{display:flex;flex-wrap:wrap;gap:2px 28px;margin:8px 0 10px;font-size:.93rem;color:var(--ink-soft)}.io b{color:var(--ink);font-weight:650}.read{line-height:1.68}.prose,.read{font-family:var(--font-read);font-size:1.1rem;max-width:var(--measure)}.prose{line-height:1.7}.prose h3{font-family:var(--font-ui);font-size:1.3rem;margin:34px 0 10px}.prose h3:first-child{margin-top:0}.prose p,.prose ul{margin:0 0 14px}.prose ul{padding-left:1.3em}.prose li{margin-bottom:6px}.callout{padding:22px 24px;background:var(--paper-2);border-radius:var(--radius)}.callout h3{margin-bottom:6px}.mistakes{margin:0;padding-left:1.2em;max-width:var(--measure);font-family:var(--font-read);font-size:1.08rem;line-height:1.6}.mistakes li{margin-bottom:10px;padding-left:4px}.video{position:relative;aspect-ratio:16/9;background:#000;border-radius:var(--radius);overflow:hidden}.video iframe{position:absolute;inset:0;width:100%;height:100%;border:0}.q{border:0;margin:0 0 32px;padding:0}.q legend{padding:0;margin-bottom:4px;font-weight:650;font-size:1.12rem;line-height:1.35}.opt{display:flex;align-items:flex-start;gap:12px;margin-top:8px;padding:12px 14px;background:var(--white);border:1.5px solid var(--line);border-radius:var(--radius);cursor:pointer}.opt:hover{border-color:var(--ink)}.opt input{margin:4px 0 0;accent-color:var(--blue);flex:none}.opt.correct{border-color:var(--teal);background:#e3f3ef}.opt.wrong{border-color:var(--bad);background:#fbebea}.q.locked .opt{cursor:default}.why{margin-top:10px;font-size:.98rem}.score{padding:20px 24px;background:var(--paper-2);border-radius:var(--radius)}.score strong{font-size:1.2rem}.score .btn-row{margin-top:14px}.tryit{background:var(--ink);color:#fff;border-radius:var(--radius);padding:32px}.tryit h2{font-size:1.7rem}.tryit p{margin-top:10px;max-width:34rem;color:#cfd9e3}.tryit .btn-row{margin-top:22px}.next{margin-top:40px;padding-top:20px;border-top:1px solid var(--line)}.tool{display:grid;grid-template-columns:minmax(0,1fr) minmax(0,1fr);grid-gap:16px 48px;gap:16px 48px;padding:32px 0;border-bottom:1px solid var(--line)}.tool h2{font-size:1.9rem}.tool .does{margin-top:8px;font-size:1.12rem}.tool ul{margin:0;padding-left:1.2em}.tool li{margin-bottom:6px}.tool .btn-row{grid-column:1/-1}.note{margin-top:36px;padding:22px 24px;background:var(--paper-2);border-radius:var(--radius);max-width:46rem}.request-grid{display:grid;grid-template-columns:minmax(0,1fr) 320px;grid-gap:64px;gap:64px;padding-top:36px}.form{display:grid;grid-gap:20px;gap:20px;max-width:600px}.field label,.field legend{display:block;margin-bottom:6px;font-weight:620;font-size:.98rem}.field legend{padding:0}.field fieldset{border:0;margin:0;padding:0}.field .hint{margin-top:4px;font-size:.88rem;color:var(--ink-soft)}.input{width:100%;min-height:46px;padding:10px 12px;border:1.5px solid var(--line);border-radius:var(--radius);background:var(--white);color:var(--ink);font:400 1rem/1.4 var(--font-ui)}.input:hover{border-color:var(--ink-soft)}.input:focus-visible{outline:3px solid var(--blue);outline-offset:1px;border-color:var(--blue)}textarea.input{min-height:120px;resize:vertical}.two{display:grid;grid-template-columns:1fr 1fr;grid-gap:20px;gap:20px}.checks{display:flex;flex-wrap:wrap;gap:8px 22px}.check{display:flex;align-items:center;gap:8px;font-weight:500;cursor:pointer}.check input{width:18px;height:18px;accent-color:var(--blue)}.error{padding:12px 14px;border-radius:var(--radius);background:#fbebea;border:1.5px solid var(--bad)}.success{padding:28px;background:#e3f3ef;border:1.5px solid var(--teal);border-radius:var(--radius);max-width:600px}.success h2{font-size:1.6rem;margin-bottom:8px}.hp{position:absolute;left:-9999px;width:1px;height:1px;overflow:hidden}.side-note{font-size:.97rem;color:var(--ink-soft)}.side-note h2{font-size:1.25rem;color:var(--ink);margin-bottom:8px}.side-note p+p,.side-note ul{margin-top:10px}.legal{max-width:var(--measure);font-family:var(--font-read);font-size:1.1rem;line-height:1.7;padding-top:24px}.legal h2{font-family:var(--font-ui);font-size:1.35rem;margin:32px 0 10px}.legal p,.legal ul{margin:0 0 12px}@media (max-width:960px){.band-grid,.hero-grid,.request-grid{grid-template-columns:minmax(0,1fr);gap:40px}.gives{grid-template-columns:repeat(2,minmax(0,1fr))}.lesson-grid{grid-template-columns:minmax(0,1fr);gap:0}.outline{display:none}}@media (max-width:680px){.fig-scroll svg{min-width:640px}.plot .axis-title,.plot .tick{font-size:21px}.plot .curve-label{font-size:23px}body{font-size:16px}.wrap{padding:0 16px}.hero{padding:36px 0 40px}.gives,.row,.tool,.two{grid-template-columns:minmax(0,1fr)}.gives{gap:24px}.steps li{padding-left:54px}.steps li:before{width:36px;height:36px}.steps li:after{left:17px;top:40px}.tryit{padding:24px 20px}.section{padding-top:56px}.band-dark{padding:48px 0}.btn-row .btn{flex:1 1 100%}.brand img{height:22px}}