:root,
html[data-theme="light"] {
  --ink: #0f2a2e;
  --ink-soft: #1c3f45;
  --paper: #f3efe6;
  --foam: #faf7f1;
  --accent: #0e8f7a;
  --accent-deep: #0a6b5c;
  --warn: #b45309;
  --danger: #b42318;
  --line: rgba(15, 42, 46, 0.12);
  --shadow: 0 18px 50px rgba(15, 42, 46, 0.08);
  --muted: rgba(15, 42, 46, 0.62);
  --footer: rgba(15, 42, 46, 0.55);
  --header-bg: rgba(250, 247, 241, 0.72);
  --card: rgba(250, 247, 241, 0.88);
  --card-strong: rgba(250, 247, 241, 0.9);
  --body-text: rgba(15, 42, 46, 0.82);
  --module-text: rgba(15, 42, 46, 0.78);
  --ok-bg: rgba(14, 143, 122, 0.12);
  --err-bg: rgba(180, 35, 24, 0.1);
  --warn-bg: rgba(180, 83, 9, 0.12);
  --pill-bg: rgba(14, 143, 122, 0.12);
  --soon-bg: rgba(180, 83, 9, 0.12);
  --btn-fg: #faf7f1;
  --btn-bg: #0f2a2e;
  --btn-bg-hover: #1c3f45;
  --ghost-hover: rgba(15, 42, 46, 0.04);
  --page-grad:
    radial-gradient(ellipse 80% 50% at 10% -10%, rgba(14, 143, 122, 0.18), transparent 55%),
    radial-gradient(ellipse 60% 40% at 100% 0%, rgba(180, 120, 60, 0.12), transparent 50%),
    linear-gradient(180deg, #efe8db 0%, #f3efe6 40%, #e7f0ee 100%);
  --radius: 18px;
  --font: "Source Sans 3", "Segoe UI", sans-serif;
  --display: "Fraunces", Georgia, serif;
  --code-fg: #1c3f45;
  --code-keyword: #0a6b5c;
  --code-string: #8a4b0f;
  --code-number: #0b5f8a;
  --code-comment: #6b7c80;
  --code-func: #1a4f8b;
  --code-type: #0e8f7a;
}

html[data-theme="dark"] {
  --ink: #e8f0ee;
  --ink-soft: #c5d5d1;
  --paper: #0d1a1c;
  --foam: #142428;
  --accent: #2ec4a7;
  --accent-deep: #5edfc4;
  --warn: #f0a35a;
  --danger: #f07167;
  --line: rgba(232, 240, 238, 0.12);
  --shadow: 0 18px 50px rgba(0, 0, 0, 0.35);
  --muted: rgba(232, 240, 238, 0.62);
  --footer: rgba(232, 240, 238, 0.5);
  --header-bg: rgba(13, 26, 28, 0.82);
  --card: rgba(20, 36, 40, 0.92);
  --card-strong: rgba(20, 36, 40, 0.95);
  --body-text: rgba(232, 240, 238, 0.85);
  --module-text: rgba(232, 240, 238, 0.78);
  --ok-bg: rgba(46, 196, 167, 0.16);
  --err-bg: rgba(240, 113, 103, 0.14);
  --warn-bg: rgba(240, 163, 90, 0.14);
  --pill-bg: rgba(46, 196, 167, 0.16);
  --soon-bg: rgba(240, 163, 90, 0.16);
  --btn-fg: #0d1a1c;
  --btn-bg: #e8f0ee;
  --btn-bg-hover: #c5d5d1;
  --ghost-hover: rgba(232, 240, 238, 0.06);
  --page-grad:
    radial-gradient(ellipse 80% 50% at 10% -10%, rgba(46, 196, 167, 0.16), transparent 55%),
    radial-gradient(ellipse 60% 40% at 100% 0%, rgba(90, 140, 160, 0.14), transparent 50%),
    linear-gradient(180deg, #0a1517 0%, #0d1a1c 45%, #102226 100%);
  --code-fg: #d7e6e2;
  --code-keyword: #5edfc4;
  --code-string: #f0a35a;
  --code-number: #7ec8ff;
  --code-comment: #8aa3a0;
  --code-func: #9ecbff;
  --code-type: #2ec4a7;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  min-height: 100vh;
  font-family: var(--font);
  color: var(--ink);
  background: var(--paper);
  line-height: 1.55;
}

.page-bg {
  position: fixed;
  inset: 0;
  z-index: -1;
  background: var(--page-grad);
}

.site-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: 1.1rem clamp(1rem, 4vw, 2.5rem);
  border-bottom: 1px solid var(--line);
  backdrop-filter: blur(8px);
  background: var(--header-bg);
  position: sticky;
  top: 0;
  z-index: 10;
}

.brand {
  font-family: var(--display);
  font-weight: 700;
  font-size: 1.45rem;
  letter-spacing: 0.04em;
  color: var(--ink);
  text-decoration: none;
}

.nav {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.85rem 1.1rem;
  font-size: 0.95rem;
}

.nav a {
  color: var(--ink-soft);
  text-decoration: none;
  font-weight: 500;
}

.nav a:hover { color: var(--accent-deep); }

.nav a.btn-nav {
  color: var(--btn-fg);
  background: var(--btn-bg);
}

.nav a.btn-nav:hover {
  color: var(--btn-fg);
  background: var(--btn-bg-hover);
}

.inline { display: inline; margin: 0; }

.linkish {
  background: none;
  border: none;
  padding: 0;
  color: var(--ink-soft);
  font: inherit;
  font-weight: 500;
  cursor: pointer;
}

.linkish:hover { color: var(--accent-deep); }

.theme-toggle {
  border: 1px solid var(--line);
  background: var(--card);
  color: var(--ink-soft);
  font: inherit;
  font-size: 0.85rem;
  font-weight: 600;
  padding: 0.35rem 0.75rem;
  border-radius: 999px;
  cursor: pointer;
}

.theme-toggle:hover {
  color: var(--accent-deep);
  border-color: var(--accent);
}

html[data-theme="light"] .theme-toggle-label[data-when="dark"],
html[data-theme="dark"] .theme-toggle-label[data-when="light"] {
  display: none;
}

.main {
  width: min(960px, calc(100% - 2rem));
  margin: 0 auto;
  padding: 2rem 0 4rem;
}

.site-footer {
  width: min(960px, calc(100% - 2rem));
  margin: 0 auto 2rem;
  padding-top: 1rem;
  border-top: 1px solid var(--line);
  color: var(--footer);
  font-size: 0.9rem;
}

.hero {
  padding: clamp(2rem, 6vw, 4.5rem) 0 2.5rem;
  animation: rise 0.7s ease both;
}

.eyebrow {
  text-transform: uppercase;
  letter-spacing: 0.16em;
  font-size: 0.78rem;
  font-weight: 600;
  color: var(--accent-deep);
  margin: 0 0 0.75rem;
}

.hero-brand {
  font-family: var(--display);
  font-size: clamp(3.4rem, 10vw, 6rem);
  line-height: 0.95;
  margin: 0;
  letter-spacing: 0.02em;
}

.hero-title {
  margin: 0.85rem 0 0;
  font-size: clamp(1.15rem, 2.4vw, 1.45rem);
  font-weight: 600;
  color: var(--ink-soft);
}

.lede {
  max-width: 36rem;
  margin: 1.25rem 0 0;
  font-size: 1.15rem;
  color: var(--body-text);
}

.hero-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  margin-top: 1.75rem;
}

.band {
  margin-top: 2.75rem;
  padding-top: 0.5rem;
  animation: rise 0.8s ease both;
  animation-delay: 0.08s;
}

.band h2, .narrow h1, .band h1 {
  font-family: var(--display);
  font-weight: 600;
  letter-spacing: -0.01em;
  margin: 0 0 0.85rem;
}

.facts {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 1.5rem;
  padding: 1.5rem;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
}

.plain {
  margin: 0;
  padding-left: 1.1rem;
}

.outcomes {
  margin: 0;
  padding: 0;
  list-style: none;
  display: grid;
  gap: 0.75rem;
}

.outcomes li {
  padding: 0.95rem 1.1rem;
  background: var(--card);
  border-left: 3px solid var(--accent);
  border-radius: 0 12px 12px 0;
}

.section-head { margin-bottom: 1.25rem; }

.muted { color: var(--muted); margin: 0.35rem 0 0; }

.note-block {
  margin-top: 1.1rem;
  padding: 0.9rem 1.1rem;
  background: var(--card);
  border-radius: 12px;
  border: 1px solid var(--line);
}

.note-block a {
  color: var(--accent-deep);
  font-weight: 600;
  text-underline-offset: 0.15em;
}

.note-block a:hover {
  color: var(--accent);
}

.module-list {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  gap: 0.85rem;
}

.module-row {
  display: grid;
  grid-template-columns: auto 1fr;
  gap: 1rem;
  padding: 1.1rem 1.2rem;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  transition: transform 0.2s ease, box-shadow 0.2s ease, border-color 0.2s ease;
}

.module-row:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow);
}

.module-row.locked { opacity: 0.92; }

a.block-link {
  text-decoration: none;
  color: inherit;
  cursor: pointer;
}

a.block-link:visited,
a.block-link:active,
a.block-link:hover {
  color: inherit;
  text-decoration: none;
}

a.block-link:hover {
  border-color: color-mix(in srgb, var(--accent) 45%, var(--line));
}

a.block-link h3 {
  color: var(--ink);
}

a.block-link:hover h3 {
  color: var(--accent-deep);
}

.module-num {
  font-family: var(--display);
  font-size: 1.5rem;
  color: var(--accent-deep);
  min-width: 2.2rem;
}

.module-top {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  gap: 0.5rem 0.85rem;
}

.module-top h3 {
  margin: 0;
  font-size: 1.12rem;
}

.module-body p {
  margin: 0.45rem 0 0;
  color: var(--module-text);
}

.module-topics {
  margin: 0.7rem 0 0;
  padding-left: 1.15rem;
  color: var(--module-text);
  display: grid;
  gap: 0.28rem;
}

.module-topics li {
  padding-left: 0.15rem;
}

.title-link {
  color: var(--ink);
  text-decoration: none;
}

.title-link:visited,
.title-link:hover {
  color: var(--accent-deep);
  text-decoration: none;
}

.crumbs {
  display: flex;
  flex-wrap: wrap;
  gap: 0.35rem 0.5rem;
  align-items: center;
  font-size: 0.9rem;
  color: var(--muted);
  margin: 0 0 1.25rem;
}

.crumbs a {
  color: var(--accent-deep);
  text-decoration: none;
  font-weight: 600;
}

.crumbs a:hover { text-decoration: underline; text-underline-offset: 0.15em; }

.lede.tight {
  margin-top: 0.75rem;
  max-width: 40rem;
}

.goals-block h2 {
  font-family: var(--display);
  font-weight: 600;
  margin: 0 0 0.85rem;
  font-size: 1.25rem;
}

.outcomes.compact li {
  padding: 0.7rem 0.95rem;
}

.lesson-list {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  gap: 0.85rem;
}

.lesson-card {
  display: grid;
  grid-template-columns: auto 1fr;
  gap: 1rem;
  padding: 1.1rem 1.2rem;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  transition: transform 0.2s ease, box-shadow 0.2s ease, border-color 0.2s ease;
}

.lesson-card:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow);
}

.lesson-card.locked { opacity: 0.92; }

.lesson-num {
  font-family: var(--display);
  font-size: 1.6rem;
  color: var(--accent-deep);
  min-width: 1.6rem;
  line-height: 1;
}

.lesson-body p {
  margin: 0.45rem 0 0;
  color: var(--module-text);
}

.section-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 0.9rem;
  margin-top: 0.5rem;
}

.section-card {
  display: grid;
  gap: 0.45rem;
  padding: 1.15rem 1.2rem;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  text-decoration: none;
  color: inherit;
  transition: transform 0.2s ease, box-shadow 0.2s ease, border-color 0.2s ease;
}

.section-card:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow);
  border-color: color-mix(in srgb, var(--accent) 45%, var(--line));
}

.section-kicker {
  font-size: 0.75rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--accent-deep);
}

.section-card h2 {
  margin: 0;
  font-family: var(--display);
  font-size: 1.25rem;
  font-weight: 600;
}

.section-card p {
  margin: 0;
  color: var(--module-text);
  font-size: 0.95rem;
}

.section-tabs {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  margin: 0 0 1.4rem;
}

.section-tabs a {
  text-decoration: none;
  font-weight: 600;
  font-size: 0.92rem;
  color: var(--ink-soft);
  padding: 0.45rem 0.85rem;
  border-radius: 999px;
  border: 1px solid var(--line);
  background: var(--card);
}

.section-tabs a:hover {
  color: var(--accent-deep);
  border-color: var(--accent);
}

.section-tabs a.is-active {
  background: var(--btn-bg);
  color: var(--btn-fg);
  border-color: transparent;
}

.narrow-wide {
  width: min(640px, 100%);
}

.prose {
  color: var(--body-text);
  font-size: 1.05rem;
}

.prose > *:first-child { margin-top: 0; }

.prose h1, .prose h2, .prose h3, .prose h4 {
  font-family: var(--display);
  color: var(--ink);
  line-height: 1.25;
  margin: 1.6rem 0 0.7rem;
}

.prose h1 { font-size: 1.7rem; }
.prose h2 { font-size: 1.35rem; }
.prose h3 { font-size: 1.15rem; }

.prose p, .prose ul, .prose ol, .prose pre, .prose blockquote {
  margin: 0.75rem 0;
}

.prose ul, .prose ol {
  padding-left: 1.25rem;
}

.prose li + li { margin-top: 0.28rem; }

.prose a {
  color: var(--accent-deep);
  font-weight: 600;
}

.prose blockquote {
  margin-left: 0;
  padding: 0.75rem 1rem;
  border-left: 3px solid var(--accent);
  background: var(--card);
  border-radius: 0 12px 12px 0;
  color: var(--module-text);
}

.prose code {
  font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  font-size: 0.92em;
  background: var(--foam);
  padding: 0.1rem 0.35rem;
  border-radius: 6px;
  border: 1px solid var(--line);
}

.prose pre {
  overflow-x: auto;
  padding: 0.95rem 1rem;
  background: var(--foam);
  border: 1px solid var(--line);
  border-radius: 12px;
}

.prose pre code {
  background: none;
  border: none;
  padding: 0;
  font-size: 0.9rem;
}

/* C++ / code highlighting (Chroma classes) */
.prose pre.chroma,
.prose .chroma {
  color: var(--code-fg);
  background: var(--foam);
  -webkit-text-size-adjust: none;
}

.prose .chroma .err { color: var(--danger); }
.prose .chroma .k,
.prose .chroma .kc,
.prose .chroma .kd,
.prose .chroma .kn,
.prose .chroma .kp,
.prose .chroma .kr,
.prose .chroma .kt { color: var(--code-keyword); font-weight: 600; }
.prose .chroma .n,
.prose .chroma .na,
.prose .chroma .nb,
.prose .chroma .nc,
.prose .chroma .no,
.prose .chroma .nd,
.prose .chroma .ni,
.prose .chroma .ne,
.prose .chroma .nf,
.prose .chroma .nl,
.prose .chroma .nn,
.prose .chroma .nx,
.prose .chroma .py,
.prose .chroma .nt,
.prose .chroma .nv,
.prose .chroma .vc,
.prose .chroma .vg,
.prose .chroma .vi { color: var(--code-fg); }
.prose .chroma .nf { color: var(--code-func); }
.prose .chroma .nc,
.prose .chroma .nn { color: var(--code-type); }
.prose .chroma .o,
.prose .chroma .ow,
.prose .chroma .p { color: var(--code-fg); }
.prose .chroma .c,
.prose .chroma .ch,
.prose .chroma .cm,
.prose .chroma .c1,
.prose .chroma .cs,
.prose .chroma .cp,
.prose .chroma .cpf { color: var(--code-comment); font-style: italic; }
.prose .chroma .s,
.prose .chroma .sa,
.prose .chroma .sb,
.prose .chroma .sc,
.prose .chroma .dl,
.prose .chroma .sd,
.prose .chroma .s2,
.prose .chroma .se,
.prose .chroma .sh,
.prose .chroma .si,
.prose .chroma .sx,
.prose .chroma .sr,
.prose .chroma .s1,
.prose .chroma .ss { color: var(--code-string); }
.prose .chroma .m,
.prose .chroma .mb,
.prose .chroma .mf,
.prose .chroma .mh,
.prose .chroma .mi,
.prose .chroma .il,
.prose .chroma .mo { color: var(--code-number); }
.prose .chroma .bp { color: var(--muted); }
.prose .chroma .fm { color: var(--code-func); }

.prose table {
  display: block;
  overflow-x: auto;
  width: 100%;
  border: 1px solid var(--line);
  border-radius: 12px;
  background: var(--card);
}

.prose th, .prose td {
  border-bottom: 1px solid var(--line);
}

.prose hr {
  border: none;
  border-top: 1px solid var(--line);
  margin: 1.5rem 0;
}

.content-body {
  padding: 1.25rem 1.35rem;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--radius);
}

.pill {
  display: inline-flex;
  align-items: center;
  font-size: 0.78rem;
  font-weight: 600;
  padding: 0.2rem 0.55rem;
  border-radius: 999px;
  background: var(--pill-bg);
  color: var(--accent-deep);
}

.pill.soon {
  background: var(--soon-bg);
  color: var(--warn);
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.35rem;
  border: none;
  border-radius: 999px;
  padding: 0.7rem 1.2rem;
  background: var(--btn-bg);
  color: var(--btn-fg);
  text-decoration: none;
  font: inherit;
  font-weight: 600;
  cursor: pointer;
  transition: background 0.15s ease, transform 0.15s ease;
}

.btn:hover { background: var(--btn-bg-hover); transform: translateY(-1px); }

.btn-ghost {
  background: transparent;
  color: var(--ink);
  border: 1px solid var(--line);
}

.btn-ghost:hover { background: var(--ghost-hover); }

.btn-small { padding: 0.4rem 0.85rem; font-size: 0.9rem; }

.btn-danger {
  background: transparent;
  color: var(--danger);
  border: 1px solid color-mix(in srgb, var(--danger) 35%, transparent);
}

.btn-danger:hover { background: var(--err-bg); }

.narrow {
  width: min(420px, 100%);
  margin: 1rem auto 0;
  padding: 1.5rem;
  background: var(--card-strong);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
}

.stack {
  display: grid;
  gap: 0.9rem;
  margin-top: 1.2rem;
}

label {
  display: grid;
  gap: 0.35rem;
  font-weight: 600;
  font-size: 0.92rem;
}

input {
  font: inherit;
  padding: 0.65rem 0.75rem;
  border-radius: 12px;
  border: 1px solid var(--line);
  background: var(--foam);
  color: var(--ink);
}

input:focus {
  outline: 2px solid color-mix(in srgb, var(--accent) 40%, transparent);
  border-color: var(--accent);
}

.banner {
  padding: 0.85rem 1rem;
  border-radius: 12px;
  margin-bottom: 1rem;
  font-weight: 500;
}

.banner.ok {
  background: var(--ok-bg);
  color: var(--accent-deep);
}

.banner.err {
  background: var(--err-bg);
  color: var(--danger);
}

.banner.warn {
  background: var(--warn-bg);
  color: var(--warn);
  margin-bottom: 1rem;
}

.temp-box {
  padding: 1rem 1.1rem;
  margin-bottom: 1.25rem;
  border-radius: var(--radius);
  background: var(--ok-bg);
  border: 1px dashed color-mix(in srgb, var(--accent) 45%, transparent);
}

.temp-box code {
  font-size: 1.05rem;
  background: var(--foam);
  padding: 0.15rem 0.4rem;
  border-radius: 6px;
}

.create-row {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  align-items: end;
  margin-bottom: 1.5rem;
}

.create-row .grow { flex: 1 1 220px; }

.table-wrap {
  overflow-x: auto;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--card);
}

table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.95rem;
}

th, td {
  text-align: left;
  padding: 0.75rem 0.9rem;
  border-bottom: 1px solid var(--line);
  vertical-align: middle;
}

th {
  font-size: 0.8rem;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--muted);
}

tr:last-child td { border-bottom: none; }

.actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
  justify-content: flex-end;
}

@keyframes rise {
  from { opacity: 0; transform: translateY(10px); }
  to { opacity: 1; transform: translateY(0); }
}

@media (max-width: 640px) {
  .site-header { align-items: flex-start; flex-direction: column; }
  .module-row { grid-template-columns: 1fr; gap: 0.35rem; }
  .actions { justify-content: flex-start; }
}