@layer reset, base, layout, components;
@layer reset {
  *, *::before, *::after { box-sizing: border-box; }
  body, h1, h2, h3, p, figure { margin: 0; }
  [hidden] { display: none !important; }
}
@layer base {
  :root { color-scheme: light; --ink: #172e4d; --muted: #536177; --blue: #184cc9; --paper: #ffffff; --wash: #edf3fc; --line: #c7d6ea; --yellow: #ffdc70; scrollbar-color: #849dbd var(--wash); }
  html { scroll-padding-top: 2rem; }
  body { background: var(--paper); color: var(--ink); font-family: 'Avenir Next', Avenir, 'Segoe UI', sans-serif; font-size: 17px; line-height: 1.65; }
  ::selection { background: #cbdcfe; color: var(--ink); }
  a { color: var(--blue); text-underline-offset: .22em; }
  a:hover { text-decoration-thickness: 2px; }
  a:focus-visible, input:focus-visible, summary:focus-visible { outline: 3px solid var(--blue); outline-offset: 5px; }
  h1, h2, h3 { line-height: 1.12; letter-spacing: -.04em; text-wrap: balance; }
  h1 { font-size: clamp(2.6rem, 4.3vw, 4.8rem); font-weight: 750; }
  h2 { font-size: clamp(2rem, 3.8vw, 3.55rem); font-weight: 700; }
  h3 { font-size: 1.35rem; letter-spacing: -.025em; }
  p { max-width: 68ch; }
  p + p { margin-top: 1rem; }
  code, samp { font-family: 'SFMono-Regular', Consolas, 'Liberation Mono', monospace; font-size: .9em; }
  p code, li > code { padding: .1em .25em; background: var(--wash); border-radius: 3px; }
  small { font-size: .8rem; }
  input { caret-color: var(--blue); }
  input::placeholder { color: var(--muted); opacity: 1; }
  .skip { position: absolute; top: -100px; left: 1rem; z-index: 3; background: white; padding: .5rem 1rem; }
  .skip:focus { top: 1rem; }
}
@layer layout {
  .site-header, main > section, .site-footer { padding-inline: max(6vw, calc((100vw - 1390px) / 2)); }
  .site-header { min-height: 88px; display: flex; align-items: center; justify-content: space-between; gap: 2rem; border-bottom: 1px solid var(--line); }
  .site-header nav { display: flex; align-items: center; gap: 1.7rem; font-size: .9rem; }
  .site-header nav a { display: inline-flex; align-items: center; min-height: 44px; color: var(--ink); text-decoration: none; }
  .hero { padding-block: 4.5rem 5rem; display: grid; grid-template-columns: 1fr 1.05fr; align-items: center; gap: 4vw; background: #f7faff; }
  .hero > *, .curriculum-top > *, .section-intro > * { min-width: 0; }
  .how-section { padding-block: 5rem; background: var(--wash); }
  .section-intro { display: grid; grid-template-columns: 1fr 1fr; gap: 5vw; align-items: start; }
  .practice-sequence { display: grid; grid-template-columns: repeat(3, 1fr); gap: 3rem; list-style: none; counter-reset: practice; padding: 0; margin: 3.5rem 0 0; }
  .practice-sequence li { counter-increment: practice; border-top: 2px solid #a7bedf; padding-top: 1.4rem; }
  .practice-sequence h3::before { content: counter(practice) '. '; color: var(--blue); }
  .practice-sequence p { margin-top: 1rem; font-size: 1rem; }
  .reasoning-section { display: grid; grid-template-columns: 1fr 1fr; gap: 7vw; padding-block: 5rem; }
  .reasoning-section h2 { margin-bottom: 1.5rem; }
  .curriculum-section { background: #f4f7fc; padding-block: 5rem; }
  .curriculum-top { display: grid; grid-template-columns: 1.2fr 1fr; gap: 6vw; align-items: end; margin-bottom: 3rem; }
  .curriculum-top p { margin-top: 1.3rem; }
  .course-list { display: grid; grid-template-columns: 1fr 1fr; column-gap: 4rem; row-gap: 2.5rem; }
  .faq-section { padding-block: 5rem; border-top: 1px solid var(--line); display: grid; grid-template-columns: .9fr 1.3fr; gap: 6vw; }
  .closing { padding-block: 5rem; background: var(--blue); color: white; }
  .closing .button { margin-block: 2rem 1rem; background: var(--yellow); color: var(--ink); }
  .closing p { font-size: 1rem; color: #e2eaff; }
  .closing a:focus-visible { outline-color: var(--yellow); }
  .site-footer { padding-block: 2rem; display: flex; align-items: center; flex-wrap: wrap; gap: 1rem 2rem; font-size: .85rem; }
  .site-footer p { flex: 1; color: var(--muted); }
  .site-footer > a { display: inline-flex; align-items: center; min-height: 44px; }
}
@layer components {
  .brand { display: inline-flex; align-items: center; min-height: 44px; gap: .7rem; font-size: 1.15rem; font-weight: 750; color: var(--ink); text-decoration: none; white-space: nowrap; }
  .brand-mark { display: inline-flex; align-items: center; justify-content: center; background: var(--blue); color: white; font: 700 1.2rem/1 'SFMono-Regular', Consolas, monospace; width: 44px; height: 44px; border-radius: 11px 11px 11px 2px; }
  .brand-mark span { color: var(--yellow); }
  .nav-practice { border-bottom: 2px solid var(--blue); padding-block: .3rem; }
  .hero-intro { font-size: 1.125rem; margin-top: 1.4rem; max-width: 38ch; }
  .button { display: inline-flex; align-items: center; justify-content: center; min-height: 48px; margin-top: 1.7rem; border: 2px solid transparent; border-radius: 7px; padding: .8rem 1.35rem; background: var(--blue); color: white; font-weight: 700; text-decoration: none; }
  .button:hover { border-color: currentColor; }
  .entry-note { margin-top: .75rem; font-size: .875rem; color: var(--muted); max-width: 40ch; }
  .hero h1 { font-size: clamp(2.2rem, 3.4vw, 3.6rem); }
  .cta-row { display: flex; flex-wrap: wrap; gap: .75rem; margin-top: 1.7rem; }
  .cta-row .button { margin-top: 0; }
  .button-secondary { background: white; color: var(--blue); border-color: var(--blue); }
  .closing .button-secondary { background: transparent; color: white; border-color: white; }
  .path { grid-template-columns: repeat(5, 1fr); gap: 1.5rem; }
  .disclaimer { font-weight: 650; color: var(--ink); }
  .worked-example { min-width: 0; border: 1px solid #a9bfde; background: white; border-radius: 12px; box-shadow: 0 12px 28px -12px #8099bc; overflow: hidden; }
  .worked-example figcaption { display: flex; flex-wrap: wrap; justify-content: space-between; gap: .25rem 1rem; align-items: center; padding: .85rem 1.2rem; font-size: .75rem; color: var(--muted); background: #f0f5ff; border-bottom: 1px solid var(--line); }
  .file-tab { color: var(--ink); font-family: 'SFMono-Regular', Consolas, monospace; }
  .example-code { padding: 1.9rem .5rem; overflow-x: auto; background: #123766; color: white; }
  .example-code ol { margin: 0; padding-left: 3rem; font-size: clamp(.8rem, 1.1vw, .95rem); line-height: 2; }
  .example-code li { padding-left: .6rem; white-space: pre; }
  .example-code li::marker { color: #b4cae5; font-size: .75rem; }
  .example-code code { font-size: 1em; background: transparent; padding: 0; color: inherit; }
  .string { color: #b7e8da; } .number { color: #ffdc70; } .fn { color: #bbd6ff; }
  .trace-flow { display: grid; grid-template-columns: 1fr auto 1fr auto 1fr auto 1fr; align-items: center; gap: .35rem; padding: 1.6rem 1rem; }
  .trace-flow > div { display: grid; justify-items: center; gap: .45rem; min-width: 0; }
  .trace-flow span:not(.flow-arrow) { font-size: .75rem; white-space: nowrap; }
  .trace-flow code { min-width: 2.5rem; text-align: center; background: var(--wash); border: 1px solid var(--line); border-radius: 5px; padding: .2rem; font-size: 1.4rem; font-weight: 700; }
  .trace-flow small { font-size: .75rem; color: var(--muted); }
  .trace-flow .trace-result code { background: var(--yellow); border-color: #ddbc5b; }
  .flow-arrow { align-self: center; color: var(--muted); }
  .example-output { margin: 0 1.2rem; border-block: 1px solid var(--line); padding: .8rem 0; display: flex; align-items: center; gap: 1.5rem; }
  .example-output span { font-size: .75rem; color: var(--muted); }
  .example-output samp { font-weight: 700; }
  .example-note { padding: 1rem 1.2rem; font-size: 1rem; color: var(--muted); }
  .practice-prompt { align-self: center; padding: 1.75rem 2rem; background: var(--wash); border: 1px solid var(--line); }
  .practice-prompt h3 { margin-bottom: 1rem; }
  .practice-prompt p { font-size: 1rem; }
  .type-comparison { width: 100%; border-collapse: collapse; margin-block: 1.5rem; text-align: left; font-variant-numeric: tabular-nums; }
  .type-comparison th, .type-comparison td { padding: .85rem .5rem; border-bottom: 1px solid var(--line); }
  .type-comparison thead th { font-size: .75rem; color: var(--muted); font-weight: 600; }
  .type-comparison tbody th { font-weight: 400; }
  .type-comparison tbody th > code, .type-comparison td code { font-size: 1.3rem; font-weight: 700; }
  .type-comparison th span { display: block; font-size: .75rem; color: var(--muted); margin-top: .2rem; }
  .type-comparison td { text-align: right; }
  .course-search label { display: block; font-size: .95rem; font-weight: 700; margin-bottom: .5rem; }
  .course-search input { min-height: 48px; width: 100%; border: 1px solid #849dbd; border-radius: 5px; background: white; color: var(--ink); padding: .9rem 1rem; font: inherit; }
  .course-search #search-status { min-height: 1.5em; margin-top: .5rem; font-size: .875rem; color: var(--muted); }
  .chapter-heading { display: flex; gap: 1rem; align-items: baseline; justify-content: space-between; border-bottom: 2px solid #9cb6dc; padding-bottom: .9rem; }
  .chapter-heading h3 { font-size: 1.4rem; }
  .chapter-heading > span { font-size: .75rem; white-space: nowrap; color: var(--muted); }
  .chapter-group ul { list-style: none; margin: 0; padding: 0; }
  .chapter-group li { border-bottom: 1px solid var(--line); }
  .chapter-group a { min-height: 44px; display: flex; gap: 1rem; justify-content: space-between; align-items: baseline; padding: .85rem 0; text-decoration: none; color: var(--ink); }
  .chapter-group a:hover span { text-decoration: underline; text-underline-offset: .2em; }
  .chapter-group small { color: var(--muted); white-space: nowrap; }
  details { border-bottom: 1px solid var(--line); }
  summary { min-height: 44px; cursor: pointer; padding-block: 1.2rem; font-weight: 650; line-height: 1.5; }
  details p { font-size: 1rem; padding: 0 0 1.3rem; color: var(--muted); }
  @media (max-width: 1050px) {
    .hero { gap: 2.5rem; padding-block: 4rem; }
    .hero h1 { font-size: clamp(2.5rem, 4.5vw, 4rem); }
    .path { grid-template-columns: repeat(2, 1fr); }
    .site-header nav { gap: 1rem; }
    .course-list { column-gap: 2rem; }
  }
  @media (max-width: 800px) {
    .site-header, main > section, .site-footer { padding-inline: 6vw; }
    .site-header { flex-wrap: wrap; gap: .25rem 1rem; padding-block: .75rem; }
    .site-header nav { width: 100%; flex-wrap: wrap; gap: 0 1rem; font-size: .8rem; }
    .hero, .section-intro, .reasoning-section, .curriculum-top, .faq-section { grid-template-columns: 1fr; }
    .hero { gap: 1.75rem; padding-block: 2rem 3rem; }
    .hero h1 { font-size: clamp(1.9rem, 8vw, 3rem); }
    .path { grid-template-columns: 1fr; }
    .hero-intro { font-size: 1rem; margin-top: 1rem; }
    .hero .button { margin-top: 1.25rem; }
    .worked-example { width: 100%; max-width: 580px; }
    .example-code { padding-block: 1.25rem; }
    .example-code ol { font-size: clamp(.8rem, 2.35vw, .95rem); }
    .practice-sequence { grid-template-columns: 1fr; gap: 2rem; margin-top: 2rem; }
    .reasoning-section, .faq-section { gap: 2rem; padding-block: 3.5rem; }
    .practice-prompt { padding: 1.4rem; }
    .curriculum-top { gap: 2rem; }
    .course-list { grid-template-columns: 1fr; }
    .how-section, .curriculum-section { padding-block: 3.5rem; }
    .section-intro { gap: 1.5rem; }
    .chapter-group a { font-size: .95rem; }
    .chapter-group small { font-size: .75rem; }
    .closing { padding-block: 3.5rem; }
  }
  @media (max-width: 380px) {
    .site-header nav { gap: 0 .75rem; font-size: .75rem; }
    .trace-flow { padding-inline: .6rem; gap: .2rem; }
    .trace-flow span:not(.flow-arrow) { white-space: normal; text-align: center; }
    .worked-example figcaption { padding-inline: 1rem; }
    .chapter-heading { flex-wrap: wrap; gap: .5rem; }
  }
  @media (prefers-reduced-motion: reduce) { *, *::before, *::after { scroll-behavior: auto !important; animation: none !important; transition: none !important; } }
}

/* Archived landing composition; course content and access rules remain current. */
@layer components {
  .original-only { display: none; }
  .site-header nav { flex-wrap: wrap; justify-content: flex-end; }
  .site-header .appearance-switch { flex-shrink: 0; }

  html[data-appearance='original'] { --ink: #192244; --muted: #4c5274; --blue: #3045c5; --paper: #ffffff; --wash: #e9edff; --line: #bdc5eb; --yellow: #ffe35a; --cyan: #55e8ff; --lime: #c1f447; --pink: #ff72bd; scrollbar-color: #7986d1 var(--wash); }
  html[data-appearance='original'] ::selection { background: var(--yellow); color: var(--ink); }
  html[data-appearance='original'] :focus-visible { outline: 3px solid #6828ce; outline-offset: 5px; }
  html[data-appearance='original'] .original-only { display: block; }
  html[data-appearance='original'] .current-only { display: none; }
  html[data-appearance='original'] h1,
  html[data-appearance='original'] h2 { letter-spacing: -.04em; }
  html[data-appearance='original'] h1 { font-size: clamp(3.3rem, 6.4vw, 6rem); }
  html[data-appearance='original'] .site-header { min-height: 105px; background: #e5e9ff; border-bottom: 3px solid #4054ff; }
  html[data-appearance='original'] .brand-mark { width: 45px; height: 44px; border: 2px solid var(--ink); border-radius: 3px; background: var(--yellow); color: var(--ink); }
  html[data-appearance='original'] .brand-mark span { color: #6828ce; }
  html[data-appearance='original'] .nav-practice { border: 2px solid var(--ink); border-radius: 3px; padding: .4rem .8rem; background: var(--lime); font-weight: 750; }
  html[data-appearance='original'] .appearance-switch select { border: 2px solid #8797d4; border-radius: 3px; background: #fff; color: var(--ink); }
  html[data-appearance='original'] .hero { padding-block: 4.5rem 5rem; background: #d2f8ff; border-bottom: 3px solid #48c4df; }
  html[data-appearance='original'] .pixel-scene { display: flex; align-items: flex-end; gap: 20px; width: fit-content; margin-bottom: 1.5rem; padding: 0 12px 8px; border-bottom: 6px solid #4054ff; }
  html[data-appearance='original'] .pixel-art { display: block; flex-shrink: 0; width: 28px; height: 28px; shape-rendering: crispEdges; image-rendering: pixelated; }
  html[data-appearance='original'] .pixel-scene .pixel-snake { width: 80px; height: 80px; }
  html[data-appearance='original'] .pixel-scene .pixel-trophy { width: 48px; height: 48px; }
  html[data-appearance='original'] .pixel-scene .pixel-star { align-self: flex-start; width: 24px; height: 24px; margin-top: 5px; }
  html[data-appearance='original'] .hero-intro { font-size: 1.22rem; margin-top: 1.7rem; }
  html[data-appearance='original'] .button { gap: .65rem; margin-top: 2rem; padding-block: .85rem; border: 2px solid var(--ink); border-radius: 3px; background: var(--lime); color: var(--ink); box-shadow: 0 4px 0 var(--ink); }
  html[data-appearance='original'] .button:hover { background: #d8ff7c; }
  html[data-appearance='original'] .button:active { transform: translateY(3px); box-shadow: 0 1px 0 var(--ink); }
  html[data-appearance='original'] .entry-note { margin-top: 1rem; font-size: .875rem; }
  html[data-appearance='original'] .hero h1 { font-size: clamp(2.6rem, 4.6vw, 4.4rem); }
  html[data-appearance='original'] .cta-row { gap: 1rem; margin-top: 2rem; }
  html[data-appearance='original'] .cta-row .button { margin-top: 0; }
  html[data-appearance='original'] .button-secondary { background: #fff; }
  html[data-appearance='original'] .closing .button-secondary { background: transparent; color: white; border-color: white; box-shadow: 0 4px 0 white; }
  html[data-appearance='original'] .worked-example { border: 3px solid var(--ink); border-radius: 4px; box-shadow: 7px 7px 0 #4054ff; }
  html[data-appearance='original'] .worked-example figcaption { background: var(--pink); color: var(--ink); border-bottom: 2px solid var(--ink); font-size: .75rem; }
  html[data-appearance='original'] .file-tab { display: inline-flex; align-items: center; gap: .6rem; }
  html[data-appearance='original'] .file-tab .pixel-art { width: 24px; height: 24px; }
  html[data-appearance='original'] .example-code { background: #202440; color: #f0f2ff; }
  html[data-appearance='original'] .example-code ol { font-size: clamp(.8rem, 1.1vw, .95rem); }
  html[data-appearance='original'] .example-code li::marker { color: #bfc7e9; font-size: .75rem; }
  html[data-appearance='original'] .string { color: #c1f447; }
  html[data-appearance='original'] .number { color: #ffe35a; }
  html[data-appearance='original'] .fn { color: #74e9ff; }
  html[data-appearance='original'] .trace-flow span:not(.flow-arrow),
  html[data-appearance='original'] .trace-flow small { font-size: .75rem; }
  html[data-appearance='original'] .trace-flow code { background: #e5e9ff; border: 2px solid #99a9e7; border-radius: 3px; color: var(--ink); }
  html[data-appearance='original'] .trace-flow .trace-result code { background: var(--yellow); border-color: #a77c00; }
  html[data-appearance='original'] .example-output { border-color: #a8b4e0; }
  html[data-appearance='original'] .example-output samp { padding: .15rem .5rem; background: #d4ffb7; color: #14522c; }
  html[data-appearance='original'] .example-note { font-size: .875rem; }
  html[data-appearance='original'] .how-section { background: #e7e6ff; }
  html[data-appearance='original'] .practice-sequence li { border-top: 4px solid #7550dc; }
  html[data-appearance='original'] .practice-sequence li:nth-child(2) { border-color: #e54391; }
  html[data-appearance='original'] .practice-sequence li:nth-child(3) { border-color: #168750; }
  html[data-appearance='original'] .practice-sequence h3::before { color: #5425ac; }
  html[data-appearance='original'] .reasoning-section,
  html[data-appearance='original'] .study-section { display: grid; grid-template-columns: 1fr 1fr; gap: 7vw; padding-block: 6rem; }
  html[data-appearance='original'] .reasoning-section h2,
  html[data-appearance='original'] .study-section h2 { margin-bottom: 1.8rem; }
  html[data-appearance='original'] .practice-prompt { border: 2px solid #b89ae8; border-radius: 4px; background: #eee3ff; padding: 2rem; }
  html[data-appearance='original'] .curriculum-section { background: #fff9d9; }
  html[data-appearance='original'] .course-search input { border: 2px solid #8d75b8; border-radius: 3px; }
  html[data-appearance='original'] .course-search #search-status { font-size: .875rem; }
  html[data-appearance='original'] .chapter-heading { border-color: #3045c5; }
  html[data-appearance='original'] .chapter-heading h3 { font-size: 1.4rem; }
  html[data-appearance='original'] .chapter-group:nth-child(3n + 2) .chapter-heading { border-color: #b9367b; }
  html[data-appearance='original'] .chapter-group:nth-child(3n) .chapter-heading { border-color: #168750; }
  html[data-appearance='original'] .chapter-group li { border-color: #d9cfa3; }
  html[data-appearance='original'] .chapter-group a:hover { background: #fff0a2; }
  html[data-appearance='original'] .study-section { background: #e3ffd5; }
  html[data-appearance='original'] .study-notes { padding-top: .5rem; }
  html[data-appearance='original'] .study-notes ul { padding-left: 1.2rem; margin-block: 1.5rem; }
  html[data-appearance='original'] .study-notes li { padding-left: .4rem; margin-bottom: .7rem; }
  html[data-appearance='original'] .study-notes li::marker { color: #086540; }
  html[data-appearance='original'] .faq-section { border-color: #a3cf91; }
  html[data-appearance='original'] .questions details { border-color: #bdc5eb; }
  html[data-appearance='original'] .questions details[open] summary { color: #5425ac; }
  html[data-appearance='original'] .closing { background: #4054ff; color: #fff; }
  html[data-appearance='original'] .closing .button { margin-block: 2rem 1rem; background: var(--yellow); color: var(--ink); }
  html[data-appearance='original'] .closing .button:hover { background: #fff19b; }
  html[data-appearance='original'] .closing p { color: #fff; }
  html[data-appearance='original'] .site-footer { background: #e5e9ff; border-top: 3px solid #192244; }
  html[data-appearance='original'] .site-footer .brand-mark { display: none; }

  @media (max-width: 1050px) {
    .site-header { gap: 1rem; }
    html[data-appearance='original'] .hero { padding-block: 4rem; }
    html[data-appearance='original'] .hero h1 { font-size: clamp(2.4rem, 5vw, 4rem); }
  }
  @media (max-width: 800px) {
    .site-header nav { justify-content: flex-start; gap: .25rem 1rem; }
    .site-header .appearance-switch { margin-left: auto; }
    html[data-appearance='original'] .site-header { gap: 1rem; padding-block: 1.2rem; }
    html[data-appearance='original'] .site-header nav { gap: .65rem 1rem; }
    html[data-appearance='original'] .hero { gap: 3rem; }
    html[data-appearance='original'] .hero h1 { font-size: clamp(2rem, 8.5vw, 3.2rem); }
    html[data-appearance='original'] .hero .cta-row { margin-top: 1.5rem; }
    html[data-appearance='original'] .example-code { padding-block: 1.9rem; }
    html[data-appearance='original'] .example-code ol { font-size: clamp(.8rem, 2.35vw, .95rem); }
    html[data-appearance='original'] .reasoning-section,
    html[data-appearance='original'] .study-section { grid-template-columns: 1fr; gap: 2rem; padding-block: 3.5rem; }
    html[data-appearance='original'] .chapter-group small { font-size: .75rem; }
  }
  @media (max-width: 380px) {
    html[data-appearance='original'] .hero h1 { font-size: clamp(1.9rem, 8.5vw, 2.6rem); }
    html[data-appearance='original'] .worked-example { width: calc(100% - 9px); }
  }
}

.legal { max-width: 70ch; margin-inline: auto; padding: 2.5rem 6vw 4rem; line-height: 1.65; }
.legal h1 { font-size: clamp(2rem, 5vw, 2.75rem); line-height: 1.1; margin: 0 0 1rem; }
.legal h2 { font-size: 1.2rem; margin: 2rem 0 .5rem; }
.legal-date { font-size: .9rem; }
.site-footer nav { display: flex; flex-wrap: wrap; gap: .25rem 1.25rem; }
.site-footer nav a { display: inline-flex; align-items: center; min-height: 44px; }