/* ===========================================================
   INTRODUCTION TO R FOR WATERSHED ECOLOGY
   Aesthetic: editorial field-notebook · deep teal & cream
   =========================================================== */

:root {
  /* PALETTE — riverbed limnology: deep water, sediment, paper */
  --paper: #f5f1e8;
  --paper-warm: #ede5d3;
  --paper-deep: #e0d4ba;
  --ink: #1a2628;
  --ink-soft: #3a4a4d;
  --ink-mute: #6b7775;

  --water-deep: #0f3a3e;     /* benthic */
  --water-mid: #2a6b6f;      /* photic */
  --water-light: #5a9a9d;    /* surface */
  --water-pale: #b8d4d6;

  --sediment: #8b6f47;
  --leaf: #7a8c4f;
  --moss: #4a5a3a;
  --rust: #b34e2a;
  --signal: #c47d3a;         /* warning amber */

  /* TYPE */
  --serif: "Source Serif 4", Georgia, "Times New Roman", serif;
  --sans: "Inter", -apple-system, BlinkMacSystemFont, sans-serif;
  --mono: "JetBrains Mono", "SF Mono", Consolas, monospace;

  /* LAYOUT */
  --measure: 90ch;
  --gutter: 2rem;
  --radius: 2px;
  --radius-lg: 4px;
}

/* ====== RESET + BASE ====== */
* { box-sizing: border-box; margin: 0; padding: 0; }

html { scroll-behavior: smooth; }

body {
  font-family: var(--serif);
  font-size: 18px;
  line-height: 1.65;
  color: var(--ink);
  background: var(--paper);
  background-image:
    radial-gradient(circle at 15% 20%, rgba(42,107,111,0.04) 0, transparent 40%),
    radial-gradient(circle at 85% 70%, rgba(139,111,71,0.05) 0, transparent 40%);
  min-height: 100vh;
  overflow-x: hidden;
  font-variant-numeric: oldstyle-nums proportional-nums;
}

/* Subtle paper grain */
body::before {
  content: "";
  position: fixed;
  inset: 0;
  pointer-events: none;
  background-image: url("data:image/svg+xml,%3Csvg viewBox='0 0 200 200' xmlns='http://www.w3.org/2000/svg'%3E%3Cfilter id='n'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.85' numOctaves='3' /%3E%3CfeColorMatrix values='0 0 0 0 0.1 0 0 0 0 0.15 0 0 0 0 0.16 0 0 0 0.025 0' /%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23n)' /%3E%3C/svg%3E");
  opacity: 0.6;
  z-index: 1000;
  mix-blend-mode: multiply;
}

a { color: var(--water-deep); text-decoration-thickness: 1px; text-underline-offset: 3px; transition: color 0.15s ease; }
a:hover { color: var(--rust); }

p { margin: 0 0 1.1rem 0; }

strong { color: var(--ink); font-weight: 600; }
em { font-style: italic; }

code {
  font-family: var(--mono);
  font-size: 0.88em;
  background: var(--paper-deep);
  padding: 0.08em 0.35em;
  border-radius: var(--radius);
  color: var(--water-deep);
  font-weight: 500;
  /* Disable JetBrains Mono ligatures so <- stays as two characters,
     not a fancy arrow glyph. Critical for teaching R syntax. */
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  font-feature-settings: "liga" 0, "calt" 0, "ss01" 0, "ss02" 0, "ss03" 0, "ss04" 0, "ss05" 0, "ss06" 0, "ss07" 0, "ss08" 0, "zero" 0;
}

/* ====== PROGRESS BAR ====== */
.progress-bar {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: 2px;
  background: transparent;
  z-index: 200;
}
.progress-fill {
  height: 100%;
  background: linear-gradient(to right, var(--water-deep), var(--water-light));
  width: 0%;
  transition: width 0.1s ease;
}

/* ====== HERO ====== */
.hero {
  position: relative;
  padding: 8rem 2rem 4rem 2rem;
  overflow: hidden;
  background: linear-gradient(180deg, var(--paper) 0%, var(--paper-warm) 100%);
  border-bottom: 1px solid var(--paper-deep);
}

.hero-inner {
  max-width: 1300px;
  margin: 0 auto;
  position: relative;
  z-index: 2;
}

.hero-meta {
  display: inline-flex;
  align-items: center;
  gap: 0.7rem;
  font-family: var(--sans);
  font-size: 11px;
  letter-spacing: 0.22em;
  text-transform: uppercase;
  color: var(--water-mid);
  margin-bottom: 2rem;
  padding: 0.4rem 0.9rem;
  border: 1px solid var(--water-mid);
  border-radius: 100px;
}
.meta-tag { font-weight: 500; }
.meta-divider { color: var(--water-light); }

.hero-title {
  font-weight: 400;
  margin-bottom: 1.8rem;
}

.hero-overline {
  display: block;
  font-family: var(--sans);
  font-size: 14px;
  font-weight: 500;
  letter-spacing: 0.06em;
  color: var(--ink-mute);
  text-transform: lowercase;
  margin-bottom: 0.7rem;
}

.hero-display {
  display: block;
  font-family: var(--serif);
  font-size: clamp(3rem, 8vw, 6.5rem);
  font-weight: 400;
  line-height: 0.95;
  letter-spacing: -0.025em;
  color: var(--ink);
  font-variation-settings: "opsz" 60;
}
.hero-display em {
  font-style: italic;
  font-weight: 400;
  color: var(--water-deep);
  font-variation-settings: "opsz" 60;
}

.hero-sub {
  font-size: 1.25rem;
  line-height: 1.5;
  color: var(--ink-soft);
  max-width: 38em;
  margin-bottom: 2.5rem;
  font-style: italic;
  font-weight: 300;
}

.hero-actions {
  display: flex;
  gap: 1rem;
  flex-wrap: wrap;
}

.btn-primary, .btn-secondary {
  font-family: var(--sans);
  font-size: 14px;
  letter-spacing: 0.04em;
  font-weight: 500;
  padding: 0.85rem 1.6rem;
  border-radius: var(--radius);
  text-decoration: none;
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  transition: all 0.2s ease;
}
.btn-primary {
  background: var(--water-deep);
  color: var(--paper);
  border: 1px solid var(--water-deep);
}
.btn-primary:hover {
  background: var(--ink);
  color: var(--paper);
  transform: translateY(-1px);
}
.btn-secondary {
  background: transparent;
  color: var(--ink);
  border: 1px solid var(--ink-soft);
}
.btn-secondary:hover {
  background: var(--ink);
  color: var(--paper);
}

/* Tertiary button — quieter link-style action for secondary affordances
   like the R Markdown download. Sits next to primary/secondary in the
   hero without competing visually for the primary CTA. */
.btn-tertiary {
  font-family: var(--sans);
  font-size: 13px;
  font-weight: 500;
  letter-spacing: 0.02em;
  padding: 0.85rem 0.5rem;
  background: transparent;
  color: var(--ink-soft);
  border: none;
  border-bottom: 1px solid transparent;
  border-radius: 0;
  cursor: pointer;
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  transition: color 0.15s ease, border-color 0.15s ease;
  text-decoration: none;
}
.btn-tertiary:hover {
  color: var(--water-deep);
  border-bottom-color: var(--water-mid);
}
.btn-tertiary:focus-visible {
  outline: 2px solid var(--water-mid);
  outline-offset: 3px;
  border-radius: 2px;
}
.btn-tertiary-icon {
  font-weight: 600;
  font-size: 1.05em;
  line-height: 1;
}

.hero-stream {
  position: absolute;
  bottom: 0;
  left: 0;
  right: 0;
  width: 100%;
  height: 220px;
  z-index: 1;
}

/* ====== LAYOUT ====== */
.layout {
  display: grid;
  grid-template-columns: 240px minmax(0, 1fr);
  gap: 4rem;
  max-width: 1300px;
  margin: 0 auto;
  padding: 4rem 2rem 6rem 2rem;
  align-items: start;
}

@media (max-width: 980px) {
  .layout {
    grid-template-columns: 1fr;
    gap: 0;
    padding: 0 1rem 4rem 1rem;
  }
  .content {
    padding-top: 1.5rem;
  }
}

/* ====== TOC ====== */
.toc {
  position: sticky;
  top: 2rem;
  font-family: var(--sans);
  font-size: 13px;
  align-self: start;
}

/* The <details> wraps the whole TOC. At desktop sizes we force it open
   and hide its <summary>. At mobile we make it a real disclosure widget. */
.toc-details {
  /* Force open on desktop regardless of toggle state. We don't actually
     remove the [open] attribute — but if a user closes it accidentally
     by tapping summary, we still want it visible at desktop widths. */
}
.toc-summary {
  /* Hidden on desktop; shown on mobile */
  display: none;
}
.toc-summary::-webkit-details-marker { display: none; }
.toc-summary::marker { content: ""; }

/* The inner block: the actual scrolling list area. On desktop it's
   the only thing showing. On mobile it's the dropdown panel. */
.toc-inner {
  padding: 0 0 0 1rem;
  border-left: 1px solid var(--paper-deep);
  max-height: calc(100vh - 4rem);
  overflow-y: auto;
  overflow-x: hidden;
  scrollbar-width: thin;
  scrollbar-color: var(--paper-deep) transparent;
}
.toc-inner::-webkit-scrollbar { width: 6px; }
.toc-inner::-webkit-scrollbar-track { background: transparent; }
.toc-inner::-webkit-scrollbar-thumb {
  background: var(--paper-deep);
  border-radius: 3px;
}

/* === MOBILE / NARROW WIDTHS === */
@media (max-width: 980px) {
  .toc {
    position: sticky;
    top: 0;
    z-index: 100;
    background: var(--paper);
    /* Slight shadow when in stuck state to separate from content */
    box-shadow: 0 1px 0 var(--paper-deep), 0 4px 14px rgba(15, 58, 62, 0.06);
    margin: 0 -1rem; /* extend to viewport edges */
    border-bottom: 1px solid var(--paper-deep);
  }

  .toc-summary {
    display: flex;
    align-items: center;
    gap: 0.6rem;
    padding: 0.85rem 1.1rem;
    cursor: pointer;
    font-family: var(--sans);
    font-size: 13px;
    color: var(--ink);
    user-select: none;
    -webkit-tap-highlight-color: transparent;
    list-style: none;
  }
  .toc-summary-label {
    font-size: 10px;
    letter-spacing: 0.25em;
    text-transform: uppercase;
    color: var(--ink-mute);
    font-weight: 500;
    flex-shrink: 0;
  }
  .toc-summary-current {
    flex: 1;
    color: var(--water-deep);
    font-weight: 600;
    font-size: 13px;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
    min-width: 0;
  }
  .toc-summary-current::before {
    content: "·";
    margin-right: 0.5rem;
    color: var(--ink-mute);
    font-weight: 400;
  }
  .toc-summary-chevron {
    color: var(--water-mid);
    font-size: 12px;
    transition: transform 0.2s ease;
    flex-shrink: 0;
  }
  .toc-details[open] .toc-summary-chevron {
    transform: rotate(180deg);
  }

  .toc-inner {
    padding: 0.5rem 1.1rem 1.2rem 1.1rem;
    border-left: none;
    border-top: 1px solid var(--paper-deep);
    max-height: 60vh;
  }
  /* Visible only when details is open */
  .toc-details:not([open]) .toc-inner { display: none; }

  /* Hide the redundant inner "Contents" heading — the summary shows it */
  .toc-inner .toc-heading { display: none; }

  /* The status section is less useful in a compact dropdown.
     Hide it on mobile to keep the menu short. */
  .toc-status { display: none; }
}
.toc-heading {
  font-size: 10px;
  letter-spacing: 0.25em;
  text-transform: uppercase;
  color: var(--ink-mute);
  margin-bottom: 1rem;
  font-weight: 500;
}
.toc-list { list-style: none; }
.toc-list li { margin-bottom: 0.45rem; }
.toc-list a {
  color: var(--ink-soft);
  text-decoration: none;
  font-weight: 400;
  display: flex;
  align-items: baseline;
  gap: 0.7rem;
  transition: color 0.15s ease, background 0.15s ease;
  padding: 0.15rem 0.4rem;
  margin-left: -0.4rem;
  border-radius: var(--radius);
}
.toc-list a:hover {
  color: var(--water-deep);
  background: rgba(42, 107, 111, 0.06);
}
.toc-num {
  font-family: var(--mono);
  font-size: 10px;
  color: var(--water-light);
  font-weight: 500;
  letter-spacing: 0;
}
.toc-list a.active { color: var(--water-deep); font-weight: 500; }
.toc-list a.active .toc-num { color: var(--water-deep); }

.toc-status {
  margin-top: 2.5rem;
  padding-top: 1.5rem;
  border-top: 1px dashed var(--paper-deep);
}
.toc-status-label {
  font-size: 10px;
  letter-spacing: 0.25em;
  text-transform: uppercase;
  color: var(--ink-mute);
  margin-bottom: 0.6rem;
}
.r-status {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  font-family: var(--mono);
  font-size: 11px;
  color: var(--ink-soft);
  margin-bottom: 0.8rem;
}
.r-status-dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--signal);
  animation: pulse 1.6s ease-in-out infinite;
  flex-shrink: 0;
}
.r-status.ready .r-status-dot {
  background: var(--leaf);
  animation: none;
}
.r-status.error .r-status-dot {
  background: var(--rust);
  animation: none;
}
@keyframes pulse {
  0%, 100% { opacity: 1; transform: scale(1); }
  50% { opacity: 0.5; transform: scale(0.85); }
}
.toc-help {
  font-size: 11px;
  line-height: 1.5;
  color: var(--ink-mute);
  font-family: var(--sans);
  margin: 0;
}

/* ====== CONTENT ====== */
.content { min-width: 0; }

.content h3 {
  font-family: var(--serif);
  font-weight: 600;
  font-size: 1.35rem;
  margin: 2.4rem 0 0.8rem 0;
  color: var(--ink);
  letter-spacing: -0.01em;
  font-variation-settings: "opsz" 24;
}

.content h4 {
  font-family: var(--serif);
  font-weight: 600;
  font-size: 1.05rem;
  margin: 1.8rem 0 0.5rem 0;
  color: var(--ink);
  letter-spacing: -0.005em;
}

.content ul, .content ol {
  margin: 0 0 1.2rem 1.5rem;
  line-height: 1.6;
}
.content li { margin-bottom: 0.4rem; }

/* Keyboard key labels for keyboard-shortcut documentation */
kbd {
  font-family: var(--mono);
  font-size: 0.78em;
  background: var(--paper-deep);
  color: var(--ink);
  padding: 0.12em 0.4em;
  border-radius: var(--radius);
  border: 1px solid rgba(26, 38, 40, 0.18);
  box-shadow: 0 1px 0 rgba(26, 38, 40, 0.12);
  font-weight: 500;
  white-space: nowrap;
  font-variant-ligatures: none;
}

/* RStudio screenshot */
.rstudio-figure {
  margin: 1.6rem 0 1.4rem 0;
  width: 100%;
}
.rstudio-figure img {
  display: block;
  width: 100%;
  height: auto;
  border-radius: var(--radius-lg);
  border: 0px solid var(--paper-deep);
  box-shadow: 0 2px 12px rgba(15, 58, 62, 0.08);
}
.rstudio-figure figcaption {
  margin-top: 0.7rem;
  font-family: var(--serif);
  font-style: italic;
  font-size: 0.92rem;
  color: var(--ink-soft);
  text-align: center;
  line-height: 1.5;
}

/* RStudio pane walkthrough — numbered list with extra spacing */
.rstudio-panes {
  margin: 1.2rem 0 1.6rem 1.5rem;
  list-style: decimal;
}
.rstudio-panes > li {
  margin-bottom: 1rem;
  padding-left: 0.4rem;
  line-height: 1.6;
}
.rstudio-panes > li > strong:first-child {
  color: var(--water-deep);
}
.rstudio-panes ul {
  margin: 0.5rem 0 0.3rem 1.2rem;
  list-style: disc;
}
.rstudio-panes ul li {
  margin-bottom: 0.3rem;
  font-size: 0.95rem;
}

/* ====== ABOUT BLOCK ====== */
.callout-about {
  background: var(--paper-warm);
  border: 1px solid var(--paper-deep);
  border-left: 3px solid var(--water-mid);
  padding: 2rem 2rem 1.5rem 2rem;
  margin-bottom: 4rem;
  border-radius: var(--radius);
}
.about-title {
  font-family: var(--serif);
  font-weight: 600;
  font-size: 1.4rem;
  margin-bottom: 1.5rem;
  color: var(--ink);
}
.about-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(230px, 1fr));
  gap: 1.5rem;
  margin-bottom: 1.5rem;
}
.about-step {
  font-size: 0.95rem;
  line-height: 1.55;
  margin: 0;
  color: var(--ink-soft);
}
.about-step-num {
  display: inline-block;
  font-family: var(--mono);
  font-size: 11px;
  font-weight: 700;
  background: var(--water-deep);
  color: var(--paper);
  width: 20px;
  height: 20px;
  line-height: 20px;
  text-align: center;
  border-radius: 50%;
  margin-right: 0.5rem;
  vertical-align: 1px;
}
.about-note {
  font-size: 0.9rem;
  font-style: italic;
  color: var(--ink-mute);
  padding-top: 1rem;
  border-top: 1px dashed var(--paper-deep);
  max-width: none;
  margin: 0;
}

/* ====== CHAPTERS ====== */
.chapter {
  margin-bottom: 5rem;
  scroll-margin-top: 2rem;
}

.chapter-header {
  margin-bottom: 1.6rem;
  padding-bottom: 1.2rem;
  border-bottom: 1px solid var(--paper-deep);
  position: relative;
}
.chapter-header::after {
  content: "";
  position: absolute;
  left: 0;
  bottom: -1px;
  width: 60px;
  height: 1px;
  background: var(--water-deep);
}

.chapter-number {
  display: block;
  font-family: var(--sans);
  font-size: 11px;
  letter-spacing: 0.28em;
  text-transform: uppercase;
  color: var(--water-mid);
  margin-bottom: 0.6rem;
  font-weight: 500;
}

.chapter-title {
  font-family: var(--serif);
  font-weight: 400;
  font-size: clamp(1.8rem, 4vw, 2.6rem);
  line-height: 1.1;
  letter-spacing: -0.02em;
  color: var(--ink);
  font-variation-settings: "opsz" 48;
}

/* ====== EQUATIONS ====== */
.equation, .equation-block {
  font-family: var(--serif);
  font-style: italic;
  font-size: 1.15rem;
  text-align: center;
  padding: 1rem 1.5rem;
  margin: 1rem auto;
  background: var(--paper-warm);
  border-left: 2px solid var(--water-mid);
  border-right: 2px solid var(--water-mid);
  max-width: fit-content;
  letter-spacing: 0.02em;
  color: var(--water-deep);
}
.equation sub, .equation-block sub { font-style: normal; font-size: 0.75em; }
.equation sup, .equation-block sup { font-style: normal; font-size: 0.75em; }

/* ====== ASIDES / NOTES ====== */
.aside-note {
  background: rgba(184, 212, 214, 0.25);
  border-left: 3px solid var(--water-mid);
  padding: 1rem 1.2rem;
  margin: 1.5rem 0;
  font-size: 0.95rem;
  color: var(--ink-soft);
  border-radius: 0 var(--radius) var(--radius) 0;
}
.aside-note p {
  /* Reset paragraph max-width inside aside in case any other rule constrains it */
  max-width: none;
}
.aside-warn {
  background: rgba(196, 125, 58, 0.12);
  border-left-color: var(--signal);
}
.aside-note strong { color: var(--ink); }

/* ====== CODE CELLS ====== */
.code-cell {
  margin: 1.5rem 0;
  border: 1px solid var(--paper-deep);
  background: #fdfcf6;
  border-radius: var(--radius-lg);
  overflow: hidden;
  box-shadow: 0 1px 0 rgba(26,38,40,0.04);
}

.code-cell-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.5rem 0.75rem 0.5rem 1rem;
  background: var(--paper-warm);
  border-bottom: 1px solid var(--paper-deep);
}

.code-cell-label {
  font-family: var(--mono);
  font-size: 10px;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--ink-mute);
  font-weight: 500;
}

.run-btn {
  font-family: var(--sans);
  font-size: 12px;
  font-weight: 600;
  letter-spacing: 0.05em;
  background: var(--water-deep);
  color: var(--paper);
  border: none;
  padding: 0.4rem 0.95rem;
  border-radius: var(--radius);
  cursor: pointer;
  transition: all 0.15s ease;
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
}
.run-btn::before {
  content: "▸";
  font-size: 10px;
}
.run-btn:hover {
  background: var(--ink);
  transform: translateY(-1px);
}
.run-btn:disabled {
  background: var(--ink-mute);
  cursor: not-allowed;
  transform: none;
}
.run-btn.running {
  background: var(--signal);
}
.run-btn.running::before {
  content: "⟳";
  animation: spin 0.8s linear infinite;
}
@keyframes spin {
  to { transform: rotate(360deg); }
}

.code-editor {
  width: 100%;
  font-family: var(--mono);
  font-size: 13px;
  line-height: 1.6;
  background: transparent;
  color: var(--ink);
  border: none;
  padding: 1rem 1.2rem;
  resize: vertical;
  min-height: 60px;
  display: block;
  tab-size: 2;
  white-space: pre;
  overflow-x: auto;
  /* Disable ligatures so <- stays as two characters. */
  font-variant-ligatures: none;
  font-feature-settings: "liga" 0, "calt" 0, "ss01" 0, "ss02" 0, "ss03" 0, "ss04" 0, "ss05" 0, "ss06" 0, "ss07" 0, "ss08" 0, "zero" 0;
}
.code-editor:focus {
  outline: none;
  background: rgba(184, 212, 214, 0.08);
}

.exercise-cell .code-editor {
  background: rgba(255,255,255,0.6);
  min-height: 110px;
}
.exercise-cell .code-editor:focus {
  background: #fff;
}

.exercise-cell {
  border: 1px dashed var(--water-mid);
  background: rgba(245, 241, 232, 0.5);
}
.exercise-cell .code-cell-header {
  background: rgba(42, 107, 111, 0.08);
}
.exercise-cell .code-cell-label {
  color: var(--water-deep);
  font-weight: 600;
}

/* === Assessment-mode segmented toggle === */
.mode-toggle {
  display: inline-flex;
  align-items: stretch;
  background: rgba(255,255,255,0.7);
  border: 1px solid var(--paper-deep);
  border-radius: var(--radius);
  overflow: hidden;
  margin-right: 0.5rem;
  user-select: none;
}
.mode-toggle button {
  font-family: var(--sans);
  font-size: 11px;
  letter-spacing: 0.04em;
  font-weight: 500;
  padding: 0.35rem 0.75rem;
  border: none;
  background: transparent;
  color: var(--ink-soft);
  cursor: pointer;
  transition: all 0.12s ease;
  border-right: 1px solid var(--paper-deep);
}
.mode-toggle button:last-child {
  border-right: none;
}
.mode-toggle button:hover {
  background: rgba(42, 107, 111, 0.06);
  color: var(--ink);
}
.mode-toggle button.active {
  background: var(--water-deep);
  color: var(--paper);
  font-weight: 600;
}
.code-cell-header-actions {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
}

/* === Assessment feedback banner === */
.assessment-feedback {
  display: none;
  font-family: var(--sans);
  font-size: 13px;
  line-height: 1.5;
  padding: 0.85rem 1.1rem;
  border-top: 1px solid var(--paper-deep);
  background: var(--paper-warm);
  color: var(--ink);
}
.assessment-feedback.visible { display: block; }
.assessment-feedback.pass {
  background: linear-gradient(0deg, rgba(122, 140, 79, 0.12), rgba(122, 140, 79, 0.18));
  border-top: 2px solid var(--leaf);
  color: var(--moss);
}
.assessment-feedback.fail {
  background: linear-gradient(0deg, rgba(196, 125, 58, 0.10), rgba(196, 125, 58, 0.16));
  border-top: 2px solid var(--signal);
  color: #6e3a14;
}
.assessment-feedback .feedback-icon {
  font-weight: 700;
  margin-right: 0.5rem;
  font-size: 15px;
}
.assessment-feedback .feedback-title {
  font-weight: 600;
}
.assessment-feedback ul {
  margin: 0.4rem 0 0 1.4rem;
  padding: 0;
  font-size: 12.5px;
}
.assessment-feedback li {
  margin: 0.2rem 0;
}
.assessment-feedback code {
  font-size: 0.9em;
}

.code-output {
  display: none;
  background: #1a2628;
  color: #d4cfbd;
  font-family: var(--mono);
  font-size: 12.5px;
  line-height: 1.55;
  padding: 1rem 1.2rem;
  max-height: 600px;
  overflow: auto;
  border-top: 1px solid var(--paper-deep);
  white-space: pre-wrap;
  overflow-wrap: anywhere;
  font-variant-ligatures: none;
  font-feature-settings: "liga" 0, "calt" 0;
  width: 100%;
  box-sizing: border-box;
}
.code-output.visible { display: block; }
.code-output > div,
.code-output > span {
  display: block;
  width: 100%;
}
.code-output .ansi-error { color: #e88060; }
.code-output .ansi-warning { color: #d4a45a; }
.code-output img {
  max-width: 100%;
  background: white;
  padding: 0.5rem;
  border-radius: var(--radius);
  margin: 0.5rem 0;
  display: block;
}
.code-output .stderr {
  color: #e88060;
  font-style: italic;
  display: block;
  width: 100%;
}

/* ====== EXERCISES ====== */
.exercise {
  margin: 2.5rem 0;
  padding: 1.5rem 1.8rem;
  background: rgba(245, 241, 232, 0.7);
  border: 1px solid var(--paper-deep);
  border-radius: var(--radius-lg);
  position: relative;
}
.exercise::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  bottom: 0;
  width: 3px;
  background: var(--water-deep);
  border-radius: var(--radius-lg) 0 0 var(--radius-lg);
}
/* Code cells inside exercises extend edge-to-edge of the exercise card,
   so output and editors are as wide as those in regular sections. The
   3px accent rail and 1.8rem prompt padding still apply to surrounding
   text — only the code cell breaks out. */
.exercise > .code-cell {
  margin-left: calc(-1.8rem + 3px);
  margin-right: -1.8rem;
  border-radius: 0;
  border-left: none;
  border-right: none;
}

.exercise-header {
  display: flex;
  align-items: baseline;
  gap: 1rem;
  margin-bottom: 1rem;
  flex-wrap: wrap;
}
.exercise-tag {
  font-family: var(--sans);
  font-size: 11px;
  letter-spacing: 0.2em;
  text-transform: uppercase;
  font-weight: 600;
  background: var(--water-deep);
  color: var(--paper);
  padding: 0.3rem 0.8rem;
  border-radius: var(--radius);
}
.exercise-meta {
  font-family: var(--serif);
  font-style: italic;
  font-size: 0.95rem;
  color: var(--water-mid);
}

.exercise-prompt p {
  margin-bottom: 0.6rem;
  max-width: var(--measure);
}
.exercise-steps {
  margin: 0.6rem 0 1rem 1.8rem;
}
.exercise-steps li {
  margin-bottom: 0.3rem;
  font-size: 0.97rem;
}

.solution {
  margin-top: 1.2rem;
}
.solution > summary {
  list-style: none;
  cursor: pointer;
  display: inline-block;
}
.solution > summary::-webkit-details-marker { display: none; }
.solution-toggle {
  font-family: var(--sans);
  font-size: 13px;
  font-weight: 500;
  color: var(--water-deep);
  padding: 0.55rem 1rem;
  border: 1px solid var(--water-mid);
  border-radius: var(--radius);
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  transition: all 0.15s ease;
  background: transparent;
}
.solution-toggle::before {
  content: "+";
  font-family: var(--mono);
  font-size: 14px;
  font-weight: 600;
  display: inline-block;
  transition: transform 0.2s ease;
}
.solution[open] .solution-toggle::before {
  content: "−";
}
.solution-toggle:hover {
  background: var(--water-deep);
  color: var(--paper);
}

.solution-body {
  margin-top: 1rem;
  padding-top: 1rem;
  border-top: 1px dashed var(--paper-deep);
  animation: slideDown 0.25s ease;
}
@keyframes slideDown {
  from { opacity: 0; transform: translateY(-6px); }
  to { opacity: 1; transform: translateY(0); }
}

.explanation {
  margin-top: 1rem;
  padding: 0.8rem 1rem;
  background: rgba(184, 212, 214, 0.2);
  border-left: 2px solid var(--water-light);
  font-size: 0.95rem;
  line-height: 1.6;
  color: var(--ink-soft);
  border-radius: 0 var(--radius) var(--radius) 0;
  max-width: none;
}
.explanation strong { color: var(--ink); }

/* ====== "WHERE TO GO NEXT" GRID ====== */
.next-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 1.2rem;
  margin: 2rem 0 3rem 0;
}
.next-card {
  background: var(--paper-warm);
  padding: 1.4rem;
  border-radius: var(--radius);
  border-top: 3px solid var(--water-mid);
  transition: transform 0.2s ease, box-shadow 0.2s ease;
}
.next-card:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 18px rgba(15,58,62,0.08);
}
.next-card-tag {
  font-family: var(--sans);
  font-size: 10px;
  letter-spacing: 0.2em;
  text-transform: uppercase;
  color: var(--water-mid);
  font-weight: 600;
  margin-bottom: 0.3rem;
}
.next-card h4 {
  font-family: var(--serif);
  font-weight: 600;
  font-size: 1.15rem;
  margin-bottom: 0.5rem;
  color: var(--ink);
}
.next-card p {
  font-size: 0.92rem;
  line-height: 1.55;
  color: var(--ink-soft);
  margin: 0;
  max-width: none;
}

/* ====== CLOSING ====== */
.closing {
  margin-top: 3rem;
  padding: 2.5rem;
  text-align: center;
  background: linear-gradient(180deg, var(--paper-warm), var(--paper));
  border-radius: var(--radius-lg);
  border: 1px solid var(--paper-deep);
}
.closing-mark {
  font-family: var(--serif);
  font-size: 2rem;
  color: var(--water-deep);
  margin-bottom: 1rem;
  max-width: none;
}
.closing-text {
  font-family: var(--serif);
  font-size: 1.1rem;
  line-height: 1.7;
  font-style: italic;
  color: var(--ink-soft);
  max-width: 38em;
  margin: 0 auto 1rem auto;
}
.closing-sig {
  font-family: var(--sans);
  font-size: 13px;
  color: var(--ink-mute);
  margin: 0;
  max-width: none;
}

/* ====== FOOTER ====== */
.site-footer {
  background: var(--ink);
  color: var(--paper-deep);
  padding: 2.5rem 2rem;
  margin-top: 4rem;
}
.footer-inner {
  max-width: 1200px;
  margin: 0 auto;
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 1rem;
}
.footer-credit, .footer-license {
  font-family: var(--sans);
  font-size: 12.5px;
  margin: 0;
  letter-spacing: 0.02em;
  max-width: none;
}
.footer-credit a {
  color: var(--water-pale);
  text-decoration: underline;
  text-decoration-thickness: 1px;
  text-underline-offset: 2px;
}
.footer-credit a:hover { color: var(--paper); }
.footer-license { color: var(--ink-mute); font-style: italic; }

/* ====== UTILITIES ====== */
::selection {
  background: var(--water-mid);
  color: var(--paper);
}

/* highlight.js override to fit our palette */
.hljs {
  background: transparent !important;
  color: var(--ink) !important;
  padding: 0 !important;
}
.hljs-keyword, .hljs-built_in { color: var(--rust); font-weight: 500; }
.hljs-string { color: var(--moss); }
.hljs-number { color: var(--water-deep); }
.hljs-comment { color: var(--ink-mute); font-style: italic; }
.hljs-function .hljs-title, .hljs-title.function_ { color: var(--water-deep); }