@font-face{font-family:Fredoka;font-style:normal;font-display:swap;font-weight:300 700;src:url(/fonts/fredoka-latin-wght.woff2) format("woff2-variations"),url(/fonts/fredoka-latin-wght.woff2) format("woff2");unicode-range:U+0000-00FF,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}@font-face{font-family:Nunito;font-style:normal;font-display:swap;font-weight:200 1000;src:url(/fonts/nunito-latin-wght.woff2) format("woff2-variations"),url(/fonts/nunito-latin-wght.woff2) format("woff2");unicode-range:U+0000-00FF,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{color-scheme:light dark;--color-bg: #fff8ee;--color-bg-alt: #ffe9d4;--color-surface: #fffdf8;--color-text: #1b2356;--color-muted: #464e7e;--color-ink: #1b2356;--color-line: #e8d6c2;--color-primary: #1b2356;--color-on-primary: #fff8ee;--color-accent: #ff8a7a;--color-on-accent: #1b2356;--color-link: #0d5c78;--color-sea: #0b6b85;--color-sea-deep: #134a7a;--color-on-sea: #ffffff;--color-night: #1b2356;--color-on-night: #fff1e0;--color-on-night-muted: #c9cdec;--color-success: #17643f;--color-success-soft: #dcf5e4;--color-focus: #c2410c;--color-focus-on-dark: #ffc46b;--panel-pink: #ffd8dc;--panel-sky: #cdeffa;--panel-mint: #d5f2d9;--panel-lilac: #e6defc;--panel-butter: #ffeeb3;--diagram-a: #ff8a7a;--diagram-b: #4cb3d4;--diagram-c: #ffc94a;--diagram-empty: #fffdf8;--diagram-ink: #1b2356;--diagram-line: #1b2356;--diagram-frog: #6cc04a;--border-thin: 2px;--border-card: 3px;--focus-width: 4px;--shadow-card: 5px 6px 0 var(--color-ink);--shadow-card-hover: 7px 9px 0 var(--color-ink);--shadow-press: 2px 2px 0 var(--color-ink);--shadow-pill: 3px 3px 0 var(--color-ink);--font-display: "Fredoka", "Nunito", ui-rounded, system-ui, sans-serif;--font-body: "Nunito", ui-rounded, system-ui, -apple-system, "Segoe UI", Roboto, Arial, sans-serif;--step--1: 1rem;--step-0: 1.25rem;--step-1: clamp(1.375rem, 1.3rem + .35vw, 1.5rem);--step-2: clamp(1.75rem, 1.5rem + 1.1vw, 2.375rem);--step-3: clamp(2.25rem, 1.8rem + 2.2vw, 3.5rem);--step-4: clamp(2.6rem, 1.9rem + 3.6vw, 4.75rem);--step-num: clamp(2.5rem, 2rem + 2.5vw, 4rem);--leading-tight: 1.08;--leading-snug: 1.25;--leading-body: 1.55;--weight-body: 600;--weight-strong: 800;--weight-display: 600;--measure: 58ch;--space-1: .25rem;--space-2: .5rem;--space-3: .75rem;--space-4: 1rem;--space-5: 1.5rem;--space-6: 2rem;--space-7: 3rem;--space-8: 4rem;--space-9: 6rem;--tap: 48px;--tap-big: 64px;--container: 74rem;--gutter: 1.25rem;--wave-height: 48px;--radius-sm: 10px;--radius-md: 18px;--radius-lg: 28px;--radius-pill: 999px;--dur-instant: .01ms;--dur-fast: .14s;--dur-base: .24s;--dur-hop: .52s;--ease-out: cubic-bezier(.2, .8, .2, 1);--ease-pop: cubic-bezier(.34, 1.56, .64, 1)}:root[data-theme=light]{color-scheme:light}@media(prefers-color-scheme:dark){:root:not([data-theme=light]){color-scheme:dark;--color-bg: #12173a;--color-bg-alt: #1a2150;--color-surface: #232c63;--color-text: #fff3e4;--color-muted: #cfd2f0;--color-ink: #060920;--color-line: #2e3878;--color-primary: #ffd27a;--color-on-primary: #12173a;--color-accent: #ff8a7a;--color-on-accent: #12173a;--color-link: #8fdcf2;--color-sea: #0a4f66;--color-sea-deep: #0b2b52;--color-on-sea: #ffffff;--color-night: #080b24;--color-on-night: #fff1e0;--color-on-night-muted: #c9cdec;--color-success: #8be3ad;--color-success-soft: #173d33;--color-focus: #ffc46b;--color-focus-on-dark: #ffc46b;--panel-pink: #5a3350;--panel-sky: #1f4f6e;--panel-mint: #24533f;--panel-lilac: #3f3a78;--panel-butter: #5c4a24;--diagram-a: #ff8a7a;--diagram-b: #5cc4e6;--diagram-c: #ffcf5c;--diagram-empty: #2f3a7a;--diagram-ink: #060920;--diagram-line: #fff3e4;--diagram-frog: #7ad35a}}:root[data-theme=dark]{color-scheme:dark;--color-bg: #12173a;--color-bg-alt: #1a2150;--color-surface: #232c63;--color-text: #fff3e4;--color-muted: #cfd2f0;--color-ink: #060920;--color-line: #2e3878;--color-primary: #ffd27a;--color-on-primary: #12173a;--color-accent: #ff8a7a;--color-on-accent: #12173a;--color-link: #8fdcf2;--color-sea: #0a4f66;--color-sea-deep: #0b2b52;--color-on-sea: #ffffff;--color-night: #080b24;--color-on-night: #fff1e0;--color-on-night-muted: #c9cdec;--color-success: #8be3ad;--color-success-soft: #173d33;--color-focus: #ffc46b;--color-focus-on-dark: #ffc46b;--panel-pink: #5a3350;--panel-sky: #1f4f6e;--panel-mint: #24533f;--panel-lilac: #3f3a78;--panel-butter: #5c4a24;--diagram-a: #ff8a7a;--diagram-b: #5cc4e6;--diagram-c: #ffcf5c;--diagram-empty: #2f3a7a;--diagram-ink: #060920;--diagram-line: #fff3e4;--diagram-frog: #7ad35a}@media(prefers-reduced-motion:reduce){:root{--dur-fast: .01ms;--dur-base: .01ms;--dur-hop: .01ms}}*,*:before,*:after{box-sizing:border-box}html{-webkit-text-size-adjust:100%;text-size-adjust:100%;scroll-padding-top:var(--space-5)}body{margin:0;min-height:100vh;display:flex;flex-direction:column;font-family:var(--font-body);font-size:var(--step-0);font-weight:var(--weight-body);line-height:var(--leading-body);color:var(--color-text);background:var(--color-bg);overflow-wrap:break-word;overflow-x:clip}h1,h2,h3{font-family:var(--font-display);font-weight:var(--weight-display);line-height:var(--leading-tight);margin:0 0 var(--space-3);text-wrap:balance}h1{font-size:var(--step-3)}h2{font-size:var(--step-2)}h3{font-size:var(--step-1);line-height:var(--leading-snug)}p,ul,ol{margin:0 0 var(--space-4)}p,li{max-width:var(--measure)}strong{font-weight:var(--weight-strong)}a{color:var(--color-link);font-weight:var(--weight-strong);text-decoration-thickness:var(--border-thin);text-underline-offset:.18em}:focus-visible{outline:var(--focus-width) solid var(--color-focus);outline-offset:var(--border-thin)}main:focus{outline:none}img,svg{max-width:100%;height:auto}.skip-link{position:absolute;left:var(--space-2);top:calc(-1 * var(--space-9));z-index:10;padding:var(--space-3) var(--space-4);background:var(--color-surface);color:var(--color-text);border:var(--border-card) solid var(--color-ink);border-radius:var(--radius-md)}.skip-link:focus{top:var(--space-2)}.visually-hidden{position:absolute;width:1px;height:1px;padding:0;margin:-1px;overflow:hidden;clip:rect(0,0,0,0);white-space:nowrap;border:0}.needs-js{display:none!important}:root.js .needs-js{display:revert!important}:root.js .no-js-only{display:none!important}.container{width:100%;max-width:var(--container);margin-inline:auto;padding-inline:var(--gutter)}main{flex:1}.section{padding-block:var(--space-8)}.section__head{text-align:center;margin-bottom:var(--space-7)}.section__head p{margin-inline:auto;color:var(--color-muted);font-size:var(--step-1)}.grid{display:grid;gap:var(--space-6)}@media(min-width:40rem){.grid--2{grid-template-columns:repeat(2,minmax(0,1fr))}}@media(min-width:52rem){.grid--3{grid-template-columns:repeat(3,minmax(0,1fr))}}@media(min-width:40rem)and (max-width:51.99rem){.grid--3{grid-template-columns:repeat(2,minmax(0,1fr))}}.site-header{background:var(--color-bg);border-bottom:var(--border-card) solid var(--color-ink)}.site-header__inner{display:flex;align-items:center;gap:var(--space-3);min-height:4.5rem;padding-block:var(--space-2)}.brand{display:inline-flex;align-items:center;gap:var(--space-2);min-height:var(--tap);color:var(--color-text);text-decoration:none;font-family:var(--font-display);font-weight:var(--weight-display);font-size:var(--step-1);margin-right:auto}.brand img{flex:none;width:44px;height:44px;border-radius:var(--radius-pill);background:var(--panel-butter);border:var(--border-thin) solid var(--color-ink)}.site-nav ul{display:flex;gap:var(--space-1);margin:0;padding:0;list-style:none}.site-nav a{display:inline-flex;align-items:center;min-height:var(--tap);padding-inline:var(--space-3);border-radius:var(--radius-pill);color:var(--color-text);text-decoration:none;font-size:var(--step--1)}.site-nav a:hover{background:var(--color-bg-alt)}.site-nav a[aria-current=page]{background:var(--panel-butter);box-shadow:inset 0 0 0 var(--border-thin) var(--color-ink)}@media(max-width:30rem){.brand span{display:none}}.btn{display:inline-flex;align-items:center;justify-content:center;gap:var(--space-2);min-height:var(--tap-big);padding:var(--space-3) var(--space-6);border:var(--border-card) solid var(--color-ink);border-radius:var(--radius-pill);box-shadow:var(--shadow-pill);font-family:var(--font-display);font-size:var(--step-1);font-weight:var(--weight-display);line-height:1;text-decoration:none;cursor:pointer;transition:transform var(--dur-fast) var(--ease-out),box-shadow var(--dur-fast) var(--ease-out)}.btn:hover{transform:translate(-1px,-2px);box-shadow:var(--shadow-card)}.btn:active{transform:translate(2px,2px);box-shadow:var(--shadow-press)}.btn--primary{background:var(--color-primary);color:var(--color-on-primary)}.btn--accent{background:var(--color-accent);color:var(--color-on-accent)}.btn--plain{background:var(--color-surface);color:var(--color-text)}.btn-row{display:flex;flex-wrap:wrap;gap:var(--space-4)}.label{display:inline-flex;align-items:center;gap:var(--space-2);margin:0 0 var(--space-4);padding:var(--space-1) var(--space-4);border:var(--border-thin) solid currentColor;border-radius:var(--radius-pill);font-size:var(--step--1);font-weight:var(--weight-strong);letter-spacing:.04em;text-transform:uppercase}.chip{display:inline-block;padding:var(--space-1) var(--space-3);border:var(--border-thin) solid var(--color-ink);border-radius:var(--radius-pill);background:var(--panel-butter);color:var(--color-text);font-size:var(--step--1);font-weight:var(--weight-strong);line-height:var(--leading-snug)}.card{position:relative;display:flex;flex-direction:column;padding:var(--space-4);background:var(--color-surface);border:var(--border-card) solid var(--color-ink);border-radius:var(--radius-md);box-shadow:var(--shadow-card)}.card h3{margin:var(--space-4) 0 var(--space-2)}.card p{margin:0;color:var(--color-muted)}.card__art{display:grid;place-items:center;aspect-ratio:4 / 3;border:var(--border-thin) solid var(--color-ink);border-radius:var(--radius-sm);overflow:hidden}.card__art img{width:72%;height:auto}.card__art svg{width:86%}.card__num{position:absolute;top:var(--space-5);left:var(--space-5);z-index:1;display:grid;place-items:center;width:2.5rem;height:2.5rem;border:var(--border-thin) solid var(--color-ink);border-radius:var(--radius-pill);background:var(--color-accent);color:var(--color-on-accent);font-family:var(--font-display);font-weight:var(--weight-display)}.card__foot{display:flex;flex-wrap:wrap;gap:var(--space-2);margin-top:var(--space-4)}.card--link{transition:transform var(--dur-base) var(--ease-pop),box-shadow var(--dur-base) var(--ease-out)}.card--link:hover,.card--link:has(a:focus-visible){transform:translate(-2px,-3px) rotate(-.4deg);box-shadow:var(--shadow-card-hover)}.card--link h3 a{color:var(--color-text);text-decoration:none}.card--link h3 a:after{content:"";position:absolute;inset:0;border-radius:var(--radius-md)}.card--link h3 a:focus-visible{outline:none}.card--link:has(a:focus-visible){outline:var(--focus-width) solid var(--color-focus);outline-offset:var(--space-1)}.panel-pink{background:var(--panel-pink)}.panel-sky{background:var(--panel-sky)}.panel-mint{background:var(--panel-mint)}.panel-lilac{background:var(--panel-lilac)}.panel-butter{background:var(--panel-butter)}.band--alt{background:var(--color-bg-alt);border-block:var(--border-card) solid var(--color-ink)}.band--sea{position:relative;background:linear-gradient(180deg,var(--color-sea),var(--color-sea-deep));color:var(--color-on-sea)}.band--sea .section__head p{color:var(--color-on-sea)}.band--sea :focus-visible{outline-color:var(--color-focus-on-dark)}.band--sea .card :focus-visible,.band--sea .card:has(a:focus-visible){outline-color:var(--color-focus-on-dark)}.wave{display:block;width:100%;height:var(--wave-height)}.wave path{fill:currentColor}.wave--top{color:var(--color-sea);margin-bottom:-1px}.wave--bottom{color:var(--color-sea-deep);margin-top:-1px;transform:scaleY(-1)}.hero{padding-block:var(--space-7) var(--space-8)}.hero__inner{display:grid;gap:var(--space-6);align-items:center}@media(min-width:52rem){.hero__inner{grid-template-columns:1.15fr 1fr}}.hero h1{font-size:var(--step-4);margin-bottom:var(--space-4)}.hero h1 em{font-style:normal;background:linear-gradient(transparent 62%,var(--panel-butter) 62%)}.hero__lead{font-size:var(--step-1);color:var(--color-muted);margin-bottom:var(--space-6)}.hero__art{position:relative;max-width:30rem;margin-inline:auto;width:100%}.hero__frame{position:relative;padding:var(--space-5);background:var(--panel-sky);border:var(--border-card) solid var(--color-ink);border-radius:var(--radius-lg);box-shadow:var(--shadow-card)}.hero__frame img{display:block;width:78%;margin-inline:auto}.sticker{position:absolute;display:grid;place-items:center;min-width:3.5rem;height:3.5rem;padding-inline:var(--space-2);border:var(--border-card) solid var(--color-ink);border-radius:var(--radius-md);box-shadow:var(--shadow-pill);font-family:var(--font-display);font-weight:var(--weight-display);font-size:var(--step-2);color:var(--diagram-ink)}.sticker--1{top:8%;left:-4%;background:var(--diagram-a);transform:rotate(-8deg)}.sticker--2{top:40%;right:-5%;background:var(--diagram-c);transform:rotate(7deg)}.sticker--3{bottom:7%;left:2%;background:var(--diagram-b);transform:rotate(4deg)}.trust{display:flex;flex-wrap:wrap;gap:var(--space-2) var(--space-5);margin:var(--space-6) 0 0;padding:0;list-style:none;font-size:var(--step--1);color:var(--color-muted)}.trust li{display:inline-flex;align-items:center;gap:var(--space-2)}.trust .icon{color:var(--color-success)}.soon{display:flex;flex-wrap:wrap;align-items:center;gap:var(--space-3) var(--space-5);margin-top:var(--space-7);padding:var(--space-5) var(--space-6);background:var(--color-night);color:var(--color-on-night);border:var(--border-card) solid var(--color-ink);border-radius:var(--radius-md);box-shadow:var(--shadow-card)}.soon p{margin:0;font-family:var(--font-display);font-size:var(--step-1)}.soon ul{display:flex;flex-wrap:wrap;gap:var(--space-2);margin:0;padding:0;list-style:none}.soon li{padding:var(--space-1) var(--space-3);border:var(--border-thin) dashed var(--color-on-night-muted);border-radius:var(--radius-pill);color:var(--color-on-night-muted);font-size:var(--step--1)}.cta{display:grid;gap:var(--space-5);align-items:center;padding:var(--space-7) var(--space-6);background:var(--color-accent);color:var(--color-on-accent);border:var(--border-card) solid var(--color-ink);border-radius:var(--radius-lg);box-shadow:var(--shadow-card)}.cta h2{font-size:var(--step-3)}.cta p{font-size:var(--step-1)}.cta img{width:100%;max-width:28rem;margin-inline:auto}@media(min-width:52rem){.cta{grid-template-columns:1fr 1fr;padding:var(--space-7) var(--space-8)}}.page-hero{padding-block:var(--space-7);background:var(--color-bg-alt);border-bottom:var(--border-card) solid var(--color-ink)}.page-hero__inner{display:grid;gap:var(--space-5);align-items:center}@media(min-width:46rem){.page-hero__inner{grid-template-columns:1fr 16rem}}.page-hero__art{width:14rem;margin-inline:auto;padding:var(--space-3);border:var(--border-card) solid var(--color-ink);border-radius:var(--radius-lg);box-shadow:var(--shadow-card)}.page-hero p{font-size:var(--step-1);color:var(--color-muted)}.crumbs ol{display:flex;flex-wrap:wrap;gap:var(--space-2);margin:0 0 var(--space-4);padding:0;list-style:none;font-size:var(--step--1)}.crumbs li+li:before{content:"›";margin-right:var(--space-2);color:var(--color-muted)}.crumbs a{display:inline-flex;align-items:center;min-height:var(--tap)}.lessons{display:grid;gap:var(--space-4);margin:0;padding:0;list-style:none;counter-reset:lesson}@media(min-width:46rem){.lessons{grid-template-columns:repeat(2,minmax(0,1fr))}}.lesson{display:flex;align-items:center;gap:var(--space-4);min-height:var(--tap-big);max-width:none;padding:var(--space-3) var(--space-4);background:var(--color-surface);border:var(--border-thin) solid var(--color-ink);border-radius:var(--radius-md);counter-increment:lesson}.lesson:before{content:counter(lesson);flex:none;display:grid;place-items:center;width:2.5rem;height:2.5rem;border:var(--border-thin) solid var(--color-ink);border-radius:var(--radius-pill);background:var(--panel-butter);font-family:var(--font-display)}.lesson__text{flex:1}.lesson__title{display:block;font-weight:var(--weight-strong);line-height:var(--leading-snug)}.lesson__skill{display:block;color:var(--color-muted);font-size:var(--step--1)}.lesson .chip{flex:none}.explainer{padding:var(--space-5);background:var(--color-surface);border:var(--border-card) solid var(--color-ink);border-radius:var(--radius-lg);box-shadow:var(--shadow-card)}.explainer__stage{padding:var(--space-4);border:var(--border-thin) solid var(--color-ink);border-radius:var(--radius-md)}.explainer__stage svg{display:block;width:100%}.explainer__readout{margin:var(--space-4) 0 0;max-width:none;text-align:center;font-family:var(--font-display);font-size:var(--step-2);line-height:var(--leading-snug)}.explainer__readout b{font-weight:var(--weight-display);font-size:var(--step-num)}.explainer__controls{display:flex;flex-wrap:wrap;justify-content:center;gap:var(--space-3);margin-top:var(--space-5)}.tool{display:inline-flex;align-items:center;justify-content:center;gap:var(--space-2);min-width:var(--tap-big);min-height:var(--tap-big);padding:var(--space-2) var(--space-5);border:var(--border-card) solid var(--color-ink);border-radius:var(--radius-pill);background:var(--color-surface);color:var(--color-text);box-shadow:var(--shadow-pill);font:inherit;font-family:var(--font-display);font-size:var(--step-1);font-weight:var(--weight-display);cursor:pointer;transition:transform var(--dur-fast) var(--ease-out),box-shadow var(--dur-fast) var(--ease-out)}.tool:active{transform:translate(2px,2px);box-shadow:var(--shadow-press)}.tool:disabled{opacity:.5;cursor:not-allowed}.tool--go{background:var(--color-accent);color:var(--color-on-accent)}.tool[aria-pressed=true]{background:var(--diagram-c);color:var(--diagram-ink)}.stepper{display:inline-flex;align-items:center;gap:var(--space-2);margin:0;padding:var(--space-2) var(--space-3);border:var(--border-thin) solid var(--color-ink);border-radius:var(--radius-pill);background:var(--color-bg)}.stepper__label{padding-inline:var(--space-2);font-weight:var(--weight-strong)}.stepper output{min-width:2ch;text-align:center;font-family:var(--font-display);font-size:var(--step-2)}.stepper .tool{min-width:var(--tap);min-height:var(--tap);padding:0;box-shadow:none}.slider{display:grid;gap:var(--space-2);width:100%;max-width:28rem;font-weight:var(--weight-strong);text-align:center}.slider input{width:100%;height:var(--tap);accent-color:var(--diagram-a);cursor:pointer}.choice{display:inline-flex;flex-wrap:wrap;justify-content:center;gap:var(--space-2);margin:0;padding:0;border:0}.choice legend{width:100%;margin-bottom:var(--space-2);text-align:center;font-weight:var(--weight-strong)}.frame-grid{display:grid;grid-template-columns:repeat(5,minmax(0,1fr));gap:var(--space-2);max-width:34rem;margin-inline:auto}.cell{display:grid;place-items:center;aspect-ratio:1;min-height:var(--tap);padding:0;border:var(--border-card) solid var(--diagram-line);border-radius:var(--radius-sm);background:var(--diagram-empty);color:var(--diagram-ink);font:inherit;cursor:pointer}.cell svg{width:72%}.cell circle{fill:var(--diagram-a);stroke:var(--diagram-ink);stroke-width:6;transform-origin:center;animation:pop var(--dur-base) var(--ease-pop)}.hundred{display:grid;grid-template-columns:repeat(10,minmax(0,1fr));gap:var(--space-1);margin:0;padding:0;list-style:none}.hundred li{display:grid;place-items:center;aspect-ratio:1;max-width:none;border:var(--border-thin) solid var(--diagram-line);border-radius:var(--radius-sm);background:var(--diagram-empty);color:var(--color-text);font-size:clamp(.8rem,.55rem + 1.2vw,1.25rem);font-weight:var(--weight-strong);font-variant-numeric:tabular-nums}.hundred li.is-on{background:var(--diagram-c);color:var(--diagram-ink)}.hundred li.is-now{background:var(--diagram-a);color:var(--diagram-ink);animation:pop var(--dur-base) var(--ease-pop)}.d-line{stroke:var(--diagram-line);stroke-width:3;stroke-linecap:round;fill:none}.d-text{fill:var(--color-text);font-family:var(--font-display);font-weight:var(--weight-display)}.d-ink{fill:var(--diagram-ink);font-family:var(--font-display);font-weight:var(--weight-display)}.d-a,.d-b,.d-c,.d-empty,.d-frog{stroke:var(--diagram-line);stroke-width:3}.d-a{fill:var(--diagram-a)}.d-b{fill:var(--diagram-b)}.d-c{fill:var(--diagram-c)}.d-empty{fill:var(--diagram-empty)}.d-frog{fill:var(--diagram-frog)}.d-hop{stroke:var(--diagram-a);stroke-width:4;stroke-dasharray:8 6;fill:none}.d-move,.d-beam{transition:transform var(--dur-hop) var(--ease-pop)}.explain-note{margin-top:var(--space-6);padding:var(--space-5);background:var(--color-bg-alt);border:var(--border-thin) solid var(--color-ink);border-radius:var(--radius-md)}.explain-note h2{font-size:var(--step-1)}.explain-note p:last-child,.explain-note ul:last-child{margin-bottom:0}.prose{max-width:46rem;padding-block:var(--space-7) var(--space-8)}.prose h2{margin-top:var(--space-7)}.prose li{margin-bottom:var(--space-2)}.site-footer{margin-top:var(--space-8);padding-block:var(--space-8) var(--space-6);background:var(--color-night);color:var(--color-on-night);border-top:var(--border-card) solid var(--color-ink)}.site-footer :focus-visible{outline-color:var(--color-focus-on-dark)}.site-footer a{color:var(--color-on-night)}.site-footer__grid{display:grid;gap:var(--space-6)}@media(min-width:46rem){.site-footer__grid{grid-template-columns:2fr 1fr 1fr 1fr}}.site-footer .brand{color:var(--color-on-night)}.site-footer p,.site-footer__small{color:var(--color-on-night-muted);font-size:var(--step--1)}.site-footer h2{margin-bottom:var(--space-2);color:var(--color-accent);font-size:var(--step--1);font-family:var(--font-body);font-weight:var(--weight-strong);letter-spacing:.06em;text-transform:uppercase}.site-footer ul{margin:0;padding:0;list-style:none}.site-footer li a{display:inline-flex;align-items:center;min-height:var(--tap);font-weight:var(--weight-body);text-decoration:none}.site-footer li a:hover{text-decoration:underline}.site-footer__small{margin-top:var(--space-7);padding-top:var(--space-5);border-top:var(--border-thin) solid var(--color-on-night-muted)}.flush+.site-footer{margin-top:0}.theme-switch{position:relative}:root:not([data-theme-choice]) .theme-switch{display:none}.theme-switch__button{display:inline-grid;place-items:center;width:var(--tap);height:var(--tap);padding:0;border:var(--border-thin) solid var(--color-ink);border-radius:var(--radius-pill);background:var(--color-surface);color:var(--color-text);cursor:pointer}.theme-switch__button:hover,.theme-switch__button[aria-expanded=true]{background:var(--panel-butter)}.theme-switch__icon{display:none}:root[data-theme-choice=light] .theme-switch__icon--light,:root[data-theme-choice=dark] .theme-switch__icon--dark,:root[data-theme-choice=system] .theme-switch__icon--system{display:block}.theme-switch__panel{position:absolute;z-index:30;top:calc(100% + var(--space-2));right:0;min-width:11rem;padding:var(--space-2);background:var(--color-surface);border:var(--border-card) solid var(--color-ink);border-radius:var(--radius-md);box-shadow:var(--shadow-card)}.theme-switch__panel fieldset{margin:0;padding:0;border:0}.theme-switch__panel legend{padding:var(--space-1) var(--space-3) var(--space-2);color:var(--color-muted);font-size:var(--step--1);font-weight:var(--weight-strong)}.theme-switch__option{display:flex;align-items:center;gap:var(--space-3);min-height:var(--tap);padding:0 var(--space-3);border-radius:var(--radius-sm);cursor:pointer}.theme-switch__option:hover,.theme-switch__option:has(input:checked){background:var(--color-bg-alt)}.theme-switch__option input{position:absolute;opacity:0}.theme-switch__option:has(input:focus-visible){outline:var(--focus-width) solid var(--color-focus)}@keyframes pop{0%{transform:scale(.4)}to{transform:scale(1)}}@keyframes bob{0%,to{transform:translateY(0)}50%{transform:translateY(-6px)}}.bob{animation:bob calc(var(--dur-hop) * 6) ease-in-out infinite}@media(prefers-reduced-motion:reduce){*,*:before,*:after{animation:none!important;transition-duration:var(--dur-instant)!important;scroll-behavior:auto!important}}.plain-list{margin:0;padding:0;list-style:none}.plain-list>li{max-width:none}.center{text-align:center}.center p,.center img{margin-inline:auto}.center .btn-row{justify-content:center}.stack-top{margin-top:var(--space-6)}.hero{overflow-x:clip}.site-footer__small{max-width:none}@media(max-width:39.99rem){.card__art{aspect-ratio:16 / 9}.card__art img{width:auto;height:9rem}.card__art svg{width:auto;height:8rem}.sticker--1{left:-2%}.sticker--2{right:-2%}}@media(max-width:39.99rem){[data-explainer=number-line] .explainer__stage{overflow-x:auto;overscroll-behavior-x:contain}[data-explainer=number-line] .explainer__stage svg{min-width:46rem}}.crumbs li{display:inline-flex;align-items:center}@media(max-width:30rem){.site-header__inner{gap:var(--space-1)}.site-nav a{padding-inline:var(--space-2)}}.card__art--pic{aspect-ratio:auto;min-height:7rem;padding:var(--space-4);overflow-x:auto}.card__art--pic svg{width:auto;max-width:100%;height:auto}.btn-row--center{justify-content:center}.pic__cell{fill:var(--diagram-empty);stroke:var(--diagram-line);stroke-width:2}.pic__dot{stroke:var(--diagram-line);stroke-width:2.5}.pic__dot--0{fill:var(--diagram-a)}.pic__dot--1{fill:var(--diagram-b)}.pic__dot--2{fill:var(--diagram-c)}.pic__cross,.pic__axis,.pic__hop{fill:none;stroke:var(--diagram-line);stroke-width:4;stroke-linecap:round}.pic__axis{stroke-width:3}.pic__hop{stroke-width:3;stroke-dasharray:6 6}.pic__rod{fill:var(--diagram-c);stroke:var(--diagram-line);stroke-width:2.5}.pic__seam{fill:none;stroke:var(--diagram-line);stroke-width:1.5}.pic__cube{fill:var(--diagram-b);stroke:var(--diagram-line);stroke-width:2.5}.pic__num{fill:var(--color-text);font-family:var(--font-display);font-size:18px}.practice{display:grid;gap:var(--space-5)}@media(min-width:46rem){.practice{grid-template-columns:repeat(2,minmax(0,1fr))}}.practice>.practice__item{counter-increment:q;gap:var(--space-3)}.practice{counter-reset:q}.practice__q{color:var(--color-text);font-family:var(--font-display);font-size:var(--step-1);font-weight:var(--weight-display)}.practice__q:before{content:counter(q) ". "}.reveal summary{display:inline-flex;align-items:center;min-height:var(--tap);padding:var(--space-2) var(--space-5);background:var(--color-surface);border:var(--border-card) solid var(--color-ink);border-radius:var(--radius-pill);box-shadow:var(--shadow-card);color:var(--color-text);font-family:var(--font-display);font-weight:var(--weight-display);cursor:pointer}.reveal summary:focus-visible{outline:var(--focus-width) solid var(--color-focus);outline-offset:var(--space-1)}.reveal__a{margin:var(--space-3) 0 0;color:var(--color-text);font-family:var(--font-display);font-size:var(--step-2)}a.lesson__title{color:var(--color-text);text-decoration-thickness:var(--border-thin);text-underline-offset:var(--space-1)}a.lesson__title:hover{text-decoration-color:var(--color-accent)}a.lesson__title:focus-visible{outline:var(--focus-width) solid var(--color-focus);outline-offset:var(--space-1)}