:root {
  --ink: #0b2035;
  --muted: #586979;
  --paper: #f3efe5;
  --cream: #fffaf0;
  --white: #ffffff;
  --teal: #0e9b9b;
  --coral: #f26655;
  --line: rgba(11, 32, 53, 0.16);
  --soft-teal: rgba(14, 155, 155, 0.08);
  font-family: Manrope, Inter, system-ui, sans-serif;
  color: var(--ink);
  background: var(--paper);
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  min-width: 0;
  background:
    radial-gradient(circle at 88% 7%, rgba(14, 155, 155, 0.12), transparent 28rem),
    var(--paper);
}
a { color: inherit; }
button, input, textarea { font: inherit; }
button { cursor: pointer; }

.site-header {
  min-height: 82px;
  padding: 0 max(4vw, 22px);
  display: flex;
  align-items: center;
  gap: 28px;
  border-bottom: 1px solid var(--line);
  background: rgba(243, 239, 229, 0.94);
  position: sticky;
  top: 0;
  z-index: 10;
  backdrop-filter: blur(8px);
}
.brand {
  flex: 0 0 auto;
  text-decoration: none;
  font: 650 24px Georgia, Newsreader, serif;
  letter-spacing: -0.02em;
}
.brand i { font-style: normal; color: var(--teal); }
.site-header nav {
  display: flex;
  gap: 22px;
  align-items: center;
  font-size: 13px;
}
.site-header nav a {
  text-decoration: none;
  white-space: nowrap;
  padding: 30px 0 26px;
  border-bottom: 3px solid transparent;
  color: var(--muted);
}
.site-header nav a:hover,
.site-header nav a[aria-current="page"] {
  color: var(--ink);
  border-bottom-color: var(--teal);
}

.eyebrow {
  margin: 0 0 10px;
  color: var(--teal);
  font-size: 13px;
  line-height: 1.45;
  font-weight: 750;
  letter-spacing: 0.02em;
}
h1, h2, h3 { font-family: Georgia, Newsreader, serif; }
h1, h2 { margin: 0.16em 0; line-height: 1.02; letter-spacing: -0.03em; }
h1 { font-size: clamp(50px, 7vw, 88px); }
h2 { font-size: clamp(34px, 4vw, 52px); }
h3 { font-size: 24px; margin: 10px 0; line-height: 1.15; }
.lede {
  color: var(--muted);
  font-size: 19px;
  line-height: 1.7;
  max-width: 760px;
}
.section-copy {
  max-width: 780px;
  color: var(--muted);
  font-size: 18px;
  line-height: 1.7;
}
.content-section { padding: 86px max(7vw, 28px); }
.section-heading { max-width: 900px; }
.section-heading-spaced { margin-top: 64px; }

.home-hero {
  padding: 88px max(7vw, 28px) 80px;
}
.home-hero h1 { max-width: 1050px; }
.home-hero h1 span { display: block; color: var(--teal); }
.home-hero .lede { max-width: 790px; }
.course-intro {
  max-width: 860px;
  margin: 54px 0 22px;
  color: var(--muted);
  font-size: 20px;
  line-height: 1.55;
}
.course-intro strong { color: var(--ink); }
.course-list {
  max-width: 900px;
  border-top: 1px solid var(--line);
}
.course-row {
  display: grid;
  grid-template-columns: 86px minmax(0, 1fr) auto;
  gap: 18px;
  align-items: center;
  min-height: 62px;
  padding: 14px 0;
  border-bottom: 1px solid var(--line);
  text-decoration: none;
}
.course-row:hover strong,
.course-row:hover .course-arrow { color: var(--teal); }
.course-row-start { background: rgba(255, 250, 240, 0.45); }
.course-number {
  font: 700 11px ui-monospace, SFMono-Regular, Menlo, monospace;
  letter-spacing: 0.08em;
  color: var(--coral);
}
.course-row strong { font-size: 16px; }
.start-badge,
.course-arrow {
  font-size: 13px;
  font-weight: 700;
  color: var(--teal);
}
.home-flow-section,
.home-start-section { border-top: 1px solid var(--line); }
.home-flow-section { padding-block: 68px; }
.home-start-section {
  padding-block: 62px;
  background: rgba(255, 250, 240, 0.42);
}
.home-start-section .button { margin-top: 14px; }
.text-links {
  display: flex;
  gap: 22px;
  flex-wrap: wrap;
  margin-top: 28px;
}
.text-links a {
  color: var(--teal);
  font-weight: 700;
  text-decoration: none;
}

.button,
.quiz-answer-row button,
.candidate-grid button,
.quiz-choice-row button,
.mini-workbench > button {
  display: inline-flex;
  min-height: 44px;
  align-items: center;
  justify-content: center;
  padding: 11px 17px;
  text-decoration: none;
  border: 1px solid var(--ink);
  background: transparent;
  color: var(--ink);
  font-weight: 700;
  font-size: 13px;
}
.button.primary,
.quiz-answer-row button {
  background: var(--ink);
  color: white;
}
.button.ghost { background: transparent; }

.lesson-hero {
  padding: 82px max(7vw, 28px);
  min-height: 350px;
  display: grid;
  grid-template-columns: 100px minmax(0, 1fr);
  gap: 28px;
  align-items: start;
  border-bottom: 1px solid var(--line);
}
.lesson-index {
  padding-top: 10px;
  color: var(--coral);
  font: 700 16px ui-monospace, SFMono-Regular, Menlo, monospace;
}

.primer-section {
  border-bottom: 1px solid var(--line);
  background: var(--cream);
}
.hex-table {
  width: 100%;
  max-width: 720px;
  margin-top: 30px;
  border-collapse: collapse;
  background: var(--white);
  border: 1px solid var(--line);
}
.hex-table th,
.hex-table td {
  padding: 12px 14px;
  text-align: left;
  border-bottom: 1px solid var(--line);
}
.hex-table th {
  color: var(--muted);
  font: 700 11px ui-monospace, SFMono-Regular, Menlo, monospace;
  letter-spacing: 0.08em;
}
.hex-table code,
.target-hash { font-family: ui-monospace, SFMono-Regular, Menlo, monospace; }

.precision-note,
.side-note,
.lesson-status {
  max-width: 900px;
  padding: 24px 28px;
  background: var(--soft-teal);
  border-left: 3px solid var(--teal);
}
.precision-note,
.side-note { margin-top: 42px; }
.precision-note p,
.side-note p:not(.eyebrow),
.lesson-status p:not(.eyebrow) {
  color: var(--muted);
  line-height: 1.7;
}

.workbench {
  padding: 78px max(7vw, 28px);
  background: var(--paper);
  border-bottom: 1px solid var(--line);
}
.workbench-heading {
  display: flex;
  justify-content: space-between;
  align-items: end;
  gap: 40px;
}
.workbench-heading h2 { max-width: 760px; }
.workbench-heading > p {
  max-width: 430px;
  color: var(--muted);
  line-height: 1.65;
}
.mini-workbench {
  border: 1px solid var(--line);
  background: var(--paper);
  padding: 28px;
  box-shadow: 12px 12px 0 rgba(11, 32, 53, 0.06);
}
.mini-workbench label {
  display: grid;
  gap: 8px;
  font-weight: 700;
}
.mini-workbench input,
.quiz-answer-row input {
  width: 100%;
  min-height: 48px;
  padding: 10px 12px;
  border: 1px solid var(--line);
  background: var(--white);
  color: var(--ink);
}
.byte-converter {
  max-width: 820px;
  margin-top: 38px;
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto minmax(0, 1fr);
  gap: 18px;
  align-items: end;
  background: var(--cream);
}
.byte-converter input {
  font: 700 24px ui-monospace, SFMono-Regular, Menlo, monospace;
}
.conversion-equals {
  padding-bottom: 12px;
  color: var(--coral);
  font: 700 24px Georgia, Newsreader, serif;
}
.microcopy {
  color: var(--muted);
  font-size: 13px;
  line-height: 1.6;
}
.workbench > .microcopy { margin-top: 20px; }

.planned-quiz {
  background: var(--cream);
  border-top: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
}
.exercises-box { max-width: 900px; margin-top: 32px; }
.tool-quiz + .tool-quiz {
  margin-top: 32px;
  padding-top: 28px;
  border-top: 1px solid var(--line);
}
.exercise-number {
  margin: 0 0 9px;
  color: var(--coral);
  font: 700 12px ui-monospace, SFMono-Regular, Menlo, monospace;
}
.quiz-answer-row {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  gap: 10px;
}
.quiz-feedback,
.exercise-progress {
  min-height: 24px;
  color: var(--teal);
  font-weight: 650;
  line-height: 1.5;
}
.exercise-progress {
  margin: 26px 0 0;
  padding-top: 20px;
  border-top: 1px solid var(--line);
}

.motivation-section {
  background: var(--cream);
  border-bottom: 1px solid var(--line);
}
.motivation-section h2 { max-width: 1000px; }
.prose-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 5vw;
  margin-top: 34px;
  max-width: 1080px;
}
.prose-grid p {
  color: var(--muted);
  line-height: 1.75;
  font-size: 17px;
}
.hash-tool {
  margin-top: 42px;
  padding: 30px;
  border: 1px solid var(--line);
  background: var(--cream);
  box-shadow: 12px 12px 0 rgba(11, 32, 53, 0.06);
}
.hash-tool label { display: grid; gap: 10px; }
.hash-tool label span,
.output span {
  color: var(--teal);
  font: 700 11px ui-monospace, SFMono-Regular, Menlo, monospace;
  letter-spacing: 0.1em;
}
.hash-tool textarea {
  width: 100%;
  min-height: 145px;
  resize: vertical;
  padding: 16px;
  border: 1px solid var(--line);
  background: var(--white);
  color: var(--ink);
  font: 14px/1.6 ui-monospace, SFMono-Regular, Menlo, monospace;
}
.arrow {
  padding: 14px;
  text-align: center;
  color: var(--coral);
  font-size: 30px;
}
.output {
  padding: 18px;
  border: 1px solid var(--line);
  background: var(--white);
}
.output code {
  display: block;
  margin-top: 10px;
  color: var(--ink);
  font: 14px/1.6 ui-monospace, SFMono-Regular, Menlo, monospace;
  overflow-wrap: anywhere;
}
.workbench-quiz {
  max-width: 960px;
  margin-top: 30px;
  padding: 30px;
  border: 1px solid var(--line);
  background: var(--white);
}
.workbench-quiz > p:not(.quiz-feedback) {
  color: var(--muted);
  line-height: 1.65;
}
.target-hash {
  display: block;
  padding: 14px;
  border: 1px solid var(--line);
  background: var(--paper);
  overflow-wrap: anywhere;
  font-size: 13px;
}
.candidate-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 14px;
  margin-top: 24px;
}
.candidate-grid > div {
  padding: 20px;
  border: 1px solid var(--line);
  background: var(--cream);
}
.candidate-grid > div > span {
  color: var(--coral);
  font: 800 12px ui-monospace, SFMono-Regular, Menlo, monospace;
}
.candidate-grid p { min-height: 48px; line-height: 1.55; }
.candidate-grid button:hover,
.quiz-choice-row button:hover { background: var(--soft-teal); }
.quiz-choice-row {
  display: flex;
  gap: 10px;
  align-items: center;
  flex-wrap: wrap;
  margin-top: 24px;
}
.quiz-choice-row span { margin-right: 8px; font-weight: 700; }

.principles {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 1px;
  margin-top: 42px;
  border: 1px solid var(--line);
  background: var(--line);
}
.principles article { padding: 30px; background: var(--paper); }
.principles article > span {
  color: var(--coral);
  font: 700 11px ui-monospace, SFMono-Regular, Menlo, monospace;
}
.principles p { color: var(--muted); line-height: 1.65; }

.lesson-end {
  padding-top: 56px;
  padding-bottom: 72px;
}
.lesson-status {
  margin: 0;
  background: var(--cream);
  border: 1px solid var(--line);
  border-left: 4px solid var(--coral);
}
.lesson-status-complete {
  border-left-color: var(--teal);
  background: rgba(14, 155, 155, 0.07);
}
.lesson-status h3 { margin-bottom: 8px; }
.lesson-status .hero-actions { margin-top: 22px; }
.lesson-status > .button { margin-top: 16px; }
.hero-actions {
  display: flex;
  gap: 12px;
  flex-wrap: wrap;
  margin-top: 28px;
}

.coming-section {
  padding: 78px max(7vw, 28px);
  display: grid;
  grid-template-columns: 1fr minmax(300px, 0.7fr);
  gap: 8vw;
}
.coming-section p:not(.eyebrow) { color: var(--muted); line-height: 1.7; }
.coming-section ol {
  margin: 0;
  padding: 0;
  list-style: none;
  counter-reset: goal;
}
.coming-section li {
  counter-increment: goal;
  padding: 20px 0;
  border-top: 1px solid var(--line);
  color: var(--muted);
}
.coming-section li::before {
  content: "0" counter(goal) "  ";
  color: var(--coral);
  font: 700 11px ui-monospace, SFMono-Regular, Menlo, monospace;
}

.not-found {
  min-height: 65vh;
  padding: 100px max(7vw, 28px);
}
.not-found .button { margin-top: 20px; }

footer {
  padding: 34px max(5vw, 24px);
  border-top: 1px solid var(--line);
  color: var(--muted);
  font-size: 12px;
  line-height: 1.6;
}
footer a { color: var(--ink); }
.footer-primary { margin-bottom: 10px; }
.footer-primary a { font-weight: 750; text-decoration: none; }
.footer-links {
  display: flex;
  flex-wrap: wrap;
  gap: 16px;
}
.footer-links a { text-decoration: none; }
.footer-note { margin: 12px 0 0; font-size: 11px; }

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
}

@media (max-width: 950px) {
  .workbench-heading { display: block; }
  .prose-grid { grid-template-columns: 1fr; gap: 8px; }
  .coming-section { grid-template-columns: 1fr; }
}

@media (max-width: 820px) {
  .site-header {
    position: static;
    display: block;
    min-height: 0;
    padding: 14px 18px 16px;
    backdrop-filter: none;
  }
  .brand {
    display: inline-block;
    margin-bottom: 12px;
  }
  .site-header nav {
    display: grid;
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 6px;
    width: 100%;
  }
  .site-header nav a {
    min-width: 0;
    padding: 9px 11px;
    white-space: normal;
    line-height: 1.3;
    border: 1px solid var(--line);
    background: var(--cream);
  }
  .site-header nav a:hover,
  .site-header nav a[aria-current="page"] {
    border-color: var(--teal);
    background: var(--soft-teal);
  }
}

@media (max-width: 700px) {
  h1 { font-size: clamp(44px, 13vw, 62px); }
  h2 { font-size: clamp(30px, 9vw, 42px); }
  .home-hero,
  .content-section,
  .workbench,
  .coming-section { padding-inline: 22px; }
  .home-hero { padding-block: 48px 54px; }
  .course-intro { margin-top: 42px; font-size: 18px; }
  .course-row {
    grid-template-columns: 58px minmax(0, 1fr) auto;
    gap: 10px;
    min-height: 58px;
  }
  .course-row strong { font-size: 15px; }
  .start-badge { max-width: 72px; text-align: right; }
  .home-flow-section { padding-block: 52px; }
  .home-start-section { padding-block: 48px; }
  .lesson-hero {
    grid-template-columns: 1fr;
    padding: 58px 22px;
    min-height: 0;
  }
  .lesson-index { padding: 0; }
  .principles,
  .candidate-grid { grid-template-columns: 1fr; }
  .byte-converter {
    grid-template-columns: 1fr;
    gap: 12px;
  }
  .conversion-equals {
    padding: 0;
    text-align: center;
  }
  .quiz-answer-row { grid-template-columns: 1fr; }
  .lesson-status .hero-actions { flex-direction: column; align-items: stretch; }
  .lesson-status .button { width: 100%; }
  .footer-links { gap: 10px 16px; }
}