/* ============================================================
   VEX IQ C++ Curriculum, stylesheet v2
   Palette: Pine Blue + Dry Sage + Powder Blue + Ash Brown
   Headings: Space Grotesk; body: system sans
   Includes scroll-reveal, card tilt, button ripple,
   shimmer progress bar, satisfying correct-answer animations.
   ============================================================ */

@import url('https://fonts.googleapis.com/css2?family=Space+Grotesk:wght@500;600;700&display=swap');

:root {
  /* core palette, from the coolors set */
  --bg:            #F5F1E8;
  --bg-soft:       #E8E2D2;
  --bg-cool:       #EDF2F7;
  --card:          #FFFFFF;
  --primary:       #3C787E;   /* Pine Blue */
  --primary-deep:  #2A5A60;
  --primary-soft:  #6FA0A6;
  --accent:        #685044;   /* Ash Brown */
  --sage:          #D0CD94;   /* Dry Sage, confirmation */
  --sage-deep:     #A6A26A;
  --sky:           #AEC5EB;   /* Powder Blue */
  --sky-deep:      #7FA3D4;
  --ink:           #1F1A14;
  --ink-soft:      #4A3F35;
  --muted:         #8A7D70;
  --line:          #D8CFC0;
  --code-bg:       #1F2A2C;
  --code-ink:      #DCE9EB;

  --shadow:        0 8px 24px rgba(40, 60, 65, 0.10);
  --shadow-lg:     0 20px 50px rgba(40, 60, 65, 0.18);
  --shadow-tilt:   0 18px 36px rgba(60, 120, 126, 0.25);

  --radius:        14px;
  --radius-sm:     8px;
  --max-w:         720px;

  --font-display:  'Space Grotesk', -apple-system, BlinkMacSystemFont, sans-serif;
  --font-body:     -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
}

* { box-sizing: border-box; }
html, body { margin: 0; padding: 0; }

body {
  background:
    radial-gradient(circle at 8% 4%, #DDE8F0 0%, transparent 40%),
    radial-gradient(circle at 92% 96%, #E0E4C4 0%, transparent 42%),
    var(--bg);
  color: var(--ink);
  font-family: var(--font-body);
  line-height: 1.58;
  min-height: 100vh;
  animation: fadeUp 460ms cubic-bezier(.2,.7,.3,1) both;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

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

/* ----- container ----- */
.container {
  max-width: var(--max-w);
  margin: 0 auto;
  padding: 28px 24px 96px;
}

/* ----- top bar ----- */
.topbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 6px 0 22px;
  border-bottom: 1px solid var(--line);
  margin-bottom: 26px;
}
.brand {
  font-family: var(--font-display);
  font-weight: 700;
  font-size: 18px;
  letter-spacing: -0.2px;
  color: var(--primary-deep);
  display: flex;
  align-items: center;
  gap: 10px;
}
.brand .dot {
  width: 12px; height: 12px; border-radius: 50%;
  background: var(--primary);
  box-shadow: 0 0 0 4px rgba(60, 120, 126, 0.16),
              0 0 0 8px rgba(60, 120, 126, 0.06);
  animation: pulseDot 2.6s ease-in-out infinite;
}
@keyframes pulseDot {
  0%, 100% { transform: scale(1);   box-shadow: 0 0 0 4px rgba(60, 120, 126, 0.18), 0 0 0 8px rgba(60, 120, 126, 0.06); }
  50%      { transform: scale(1.1); box-shadow: 0 0 0 6px rgba(60, 120, 126, 0.10), 0 0 0 12px rgba(60, 120, 126, 0.03); }
}
.topbar nav {
  display: flex;
  align-items: center;
  gap: 6px;
}
.topbar nav a {
  position: relative;
  color: var(--ink-soft);
  text-decoration: none;
  font-size: 14px;
  padding: 6px 8px;
  font-weight: 500;
  transition: color 180ms ease;
}
.topbar nav a::after {
  content: "";
  position: absolute;
  left: 8px; right: 8px; bottom: 2px;
  height: 2px;
  background: var(--primary);
  transform: scaleX(0);
  transform-origin: left;
  transition: transform 220ms cubic-bezier(.2,.7,.3,1);
}
.topbar nav a:hover { color: var(--primary-deep); }
.topbar nav a:hover::after { transform: scaleX(1); }

.topbar .logout-btn {
  background: transparent;
  border: 1px solid var(--line);
  color: var(--ink-soft);
  padding: 7px 12px;
  border-radius: 8px;
  font-size: 13px;
  font-family: var(--font-display);
  font-weight: 500;
  cursor: pointer;
  transition: all 180ms ease;
}
.topbar .logout-btn:hover {
  border-color: var(--primary);
  color: var(--primary-deep);
  background: var(--bg-cool);
}

/* ----- headings (display font) ----- */
h1, h2, h3, .display {
  font-family: var(--font-display);
  letter-spacing: -0.5px;
}
h1 {
  font-size: 34px;
  font-weight: 700;
  margin: 6px 0 8px;
  color: var(--ink);
  line-height: 1.15;
}
h2 {
  font-size: 22px;
  font-weight: 700;
  margin: 30px 0 10px;
  color: var(--primary-deep);
  letter-spacing: -0.3px;
}
h3 {
  font-size: 17px;
  font-weight: 600;
  margin: 20px 0 6px;
  color: var(--ink);
}
p { margin: 8px 0 14px; }
.subtitle {
  color: var(--muted);
  font-size: 15px;
  margin-top: -2px;
  margin-bottom: 14px;
}

/* ----- cards (with subtle tilt + shine) ----- */
.card {
  background: var(--card);
  border-radius: var(--radius);
  padding: 20px 22px;
  box-shadow: var(--shadow);
  border: 1px solid #ECE6D8;
  margin: 16px 0;
  position: relative;
  overflow: hidden;
  transition: transform 320ms cubic-bezier(.2,.7,.3,1),
              box-shadow 320ms ease;
}
.card::before {
  content: "";
  position: absolute;
  inset: 0;
  background: linear-gradient(120deg, transparent 30%, rgba(174,197,235,0.10) 50%, transparent 70%);
  transform: translateX(-100%);
  transition: transform 700ms ease;
  pointer-events: none;
}
.card:hover {
  transform: translateY(-3px);
  box-shadow: var(--shadow-lg);
}
.card:hover::before { transform: translateX(100%); }

/* ----- unit / lesson grid ----- */
.unit { margin: 26px 0 10px; }
.unit-header {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  margin-bottom: 10px;
}
.unit-header h2 { margin: 0; }
.unit-meta {
  font-size: 12px;
  letter-spacing: 1.2px;
  text-transform: uppercase;
  color: var(--muted);
  font-family: var(--font-display);
  font-weight: 500;
}
.lessons {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
}
@media (max-width: 560px) { .lessons { grid-template-columns: 1fr; } }

.lesson-card {
  background: linear-gradient(180deg, #FFFFFF 0%, #F7F2E5 100%);
  border: 1px solid #E2D9C5;
  border-radius: 12px;
  padding: 14px 14px 14px;
  text-decoration: none;
  color: var(--ink);
  display: block;
  position: relative;
  overflow: hidden;
  transition: transform 280ms cubic-bezier(.2,.7,.3,1.1),
              border-color 200ms ease,
              box-shadow 280ms ease;
}
.lesson-card::after {
  content: "";
  position: absolute;
  bottom: 0; left: 0; right: 0;
  height: 3px;
  background: linear-gradient(90deg, var(--primary) 0%, var(--sky-deep) 100%);
  transform: scaleX(0);
  transform-origin: left;
  transition: transform 360ms cubic-bezier(.2,.7,.3,1);
}
.lesson-card:hover {
  transform: translateY(-4px) rotate(-0.4deg);
  border-color: var(--primary);
  box-shadow: var(--shadow-tilt);
}
.lesson-card:hover::after { transform: scaleX(1); }

.lesson-card .week {
  font-family: var(--font-display);
  font-size: 11px;
  letter-spacing: 1.2px;
  text-transform: uppercase;
  color: var(--primary);
  font-weight: 600;
}
.lesson-card .title {
  font-family: var(--font-display);
  font-weight: 600;
  font-size: 15.5px;
  margin: 4px 0 0;
  letter-spacing: -0.2px;
}
.lesson-card .check {
  position: absolute;
  top: 12px; right: 12px;
  width: 22px; height: 22px;
  border-radius: 50%;
  border: 2px solid var(--line);
  background: #fff;
  display: grid; place-items: center;
  font-size: 12px;
  color: transparent;
  transition: all 280ms cubic-bezier(.2,.7,.3,1.4);
}
.lesson-card.done .check {
  background: var(--sage);
  border-color: var(--sage-deep);
  color: var(--ink);
  box-shadow: 0 0 0 6px rgba(208, 205, 148, 0.28);
  animation: checkPop 460ms cubic-bezier(.2,.7,.3,1.6);
}
.lesson-card.done .check::before {
  content: "";
  width: 5px;
  height: 9px;
  margin-top: -2px;
  border: solid var(--ink);
  border-width: 0 2px 2px 0;
  transform: rotate(45deg);
}
@keyframes checkPop {
  0%   { transform: scale(0.6) rotate(-20deg); opacity: 0; }
  60%  { transform: scale(1.15) rotate(6deg);  opacity: 1; }
  100% { transform: scale(1) rotate(0);        opacity: 1; }
}

/* ----- progress bar with shimmer ----- */
.progress-wrap {
  background: var(--bg-soft);
  border-radius: 999px;
  height: 12px;
  overflow: hidden;
  margin: 14px 0 6px;
  position: relative;
}
.progress-bar {
  height: 100%;
  background: linear-gradient(90deg, var(--primary) 0%, var(--sky-deep) 100%);
  width: 0%;
  border-radius: 999px;
  transition: width 900ms cubic-bezier(.2,.7,.3,1);
  position: relative;
  overflow: hidden;
}
.progress-bar::after {
  content: "";
  position: absolute;
  inset: 0;
  background: linear-gradient(90deg, transparent 0%, rgba(255,255,255,0.55) 50%, transparent 100%);
  animation: shimmer 2.4s linear infinite;
}
@keyframes shimmer {
  0%   { transform: translateX(-100%); }
  100% { transform: translateX(100%); }
}
.progress-text {
  font-size: 13px;
  color: var(--muted);
  font-family: var(--font-display);
  font-weight: 500;
  letter-spacing: 0.2px;
}

/* ----- code blocks ----- */
pre {
  background: var(--code-bg);
  color: var(--code-ink);
  padding: 16px 18px;
  border-radius: var(--radius-sm);
  overflow-x: auto;
  font-size: 13.5px;
  line-height: 1.6;
  font-family: 'SF Mono', Menlo, Consolas, monospace;
  border: 1px solid #2D3D40;
  position: relative;
  box-shadow: inset 0 0 0 1px rgba(255,255,255,0.04);
}
pre::before {
  content: "C++";
  position: absolute;
  top: 8px; right: 12px;
  font-size: 10px;
  letter-spacing: 1px;
  color: var(--primary-soft);
  font-family: var(--font-display);
  font-weight: 600;
}
code {
  font-family: 'SF Mono', Menlo, Consolas, monospace;
  background: rgba(60, 120, 126, 0.10);
  color: var(--accent);
  padding: 1px 6px;
  border-radius: 4px;
  font-size: 0.92em;
}
pre code { background: transparent; color: inherit; padding: 0; }

/* ----- callouts ----- */
.callout {
  border-left: 4px solid var(--primary);
  background: var(--bg-cool);
  padding: 14px 16px;
  border-radius: 6px;
  margin: 16px 0;
}
.callout.warn { border-color: var(--accent); background: #F3EBE3; }
.callout.tip  { border-color: var(--sage-deep); background: #F5F2DE; }
.callout strong { color: var(--accent); }

/* analogy boxes, special style for the "think of it like" callouts */
.analogy {
  position: relative;
  background: linear-gradient(135deg, #F0EBDB 0%, #E8E2D2 100%);
  border-left: 4px solid var(--sage-deep);
  border-radius: 8px;
  padding: 14px 16px;
  margin: 18px 0;
  font-size: 14.5px;
}
.analogy strong {
  font-family: var(--font-display);
  color: var(--primary-deep);
  font-weight: 600;
  display: block;
  margin-bottom: 4px;
  font-size: 11px;
  letter-spacing: 1.4px;
  text-transform: uppercase;
}

/* ----- resource links ----- */
.resource-list { list-style: none; padding: 0; }
.resource-list li {
  padding: 11px 14px;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 10px;
  margin-bottom: 8px;
  transition: transform 200ms cubic-bezier(.2,.7,.3,1),
              border-color 200ms ease,
              box-shadow 200ms ease;
}
.resource-list li:hover {
  transform: translateX(4px);
  border-color: var(--primary);
  box-shadow: 0 4px 14px rgba(60, 120, 126, 0.12);
}
.resource-list a {
  color: var(--primary-deep);
  text-decoration: none;
  font-weight: 600;
}
.resource-list a:hover { text-decoration: underline; }
.resource-list .kind {
  display: inline-block;
  font-family: var(--font-display);
  font-size: 10px;
  font-weight: 600;
  letter-spacing: 0.8px;
  padding: 3px 7px;
  border-radius: 4px;
  margin-right: 8px;
  vertical-align: middle;
  text-transform: uppercase;
}
.kind.video { background: rgba(104, 80, 68, 0.12); color: var(--accent); }
.kind.read  { background: rgba(208, 205, 148, 0.35); color: #6B6730; }
.kind.docs  { background: rgba(174, 197, 235, 0.40); color: #2E5A8C; }

/* ----- quiz ----- */
.quiz {
  margin-top: 32px;
  padding: 22px;
  border-radius: var(--radius);
  background: linear-gradient(180deg, #FCFAF3 0%, #F0EBDB 100%);
  border: 1px solid var(--line);
  position: relative;
  overflow: hidden;
}
.quiz::before {
  content: "";
  position: absolute;
  top: -40px; right: -40px;
  width: 120px; height: 120px;
  background: radial-gradient(circle, rgba(174,197,235,0.30) 0%, transparent 70%);
  border-radius: 50%;
}
.quiz h2 { margin-top: 0; color: var(--primary-deep); position: relative; }
.quiz-q {
  font-weight: 600;
  margin-bottom: 10px;
  font-family: var(--font-display);
  letter-spacing: -0.2px;
}
.quiz-options { display: grid; gap: 8px; margin-bottom: 14px; }

.quiz-option {
  background: #fff;
  border: 2px solid var(--line);
  border-radius: 10px;
  padding: 11px 14px;
  cursor: pointer;
  text-align: left;
  font-size: 14px;
  font-family: var(--font-body);
  color: var(--ink);
  transition: all 200ms cubic-bezier(.2,.7,.3,1);
  position: relative;
  overflow: hidden;
}
.quiz-option::before {
  content: "";
  position: absolute;
  inset: 0;
  background: radial-gradient(circle at var(--rx,50%) var(--ry,50%), rgba(60,120,126,0.18) 0%, transparent 60%);
  opacity: 0;
  transition: opacity 220ms ease;
  pointer-events: none;
}
.quiz-option:hover {
  border-color: var(--primary);
  transform: translateY(-1px);
}
.quiz-option:hover::before { opacity: 1; }
.quiz-option.correct {
  background: linear-gradient(180deg, #E8E6B8 0%, var(--sage) 100%);
  border-color: var(--sage-deep);
  color: var(--ink);
  font-weight: 700;
  animation: correctPulse 700ms cubic-bezier(.2,.7,.3,1.3);
}
.quiz-option.wrong {
  background: #F3E0DA;
  border-color: var(--accent);
  animation: shake 380ms ease;
}
.quiz-option:disabled { cursor: default; opacity: 0.7; }

@keyframes correctPulse {
  0%   { transform: scale(1);    box-shadow: 0 0 0 0  rgba(208, 205, 148, 0.85); }
  50%  { transform: scale(1.04); box-shadow: 0 0 0 16px rgba(208, 205, 148, 0); }
  100% { transform: scale(1);    box-shadow: 0 0 0 0  rgba(208, 205, 148, 0); }
}
@keyframes shake {
  0%,100% { transform: translateX(0); }
  20% { transform: translateX(-6px); }
  40% { transform: translateX(6px); }
  60% { transform: translateX(-4px); }
  80% { transform: translateX(4px); }
}

.quiz-feedback {
  min-height: 22px;
  font-size: 14px;
  margin-top: 6px;
  color: var(--ink-soft);
  font-weight: 500;
}
.quiz-feedback.good {
  color: var(--primary-deep);
  font-weight: 700;
  font-family: var(--font-display);
}

/* ----- confetti (palette colors now) ----- */
.confetti {
  position: fixed;
  pointer-events: none;
  inset: 0;
  overflow: hidden;
  z-index: 9999;
}
.confetti span {
  position: absolute;
  width: 10px; height: 14px;
  opacity: 0;
  animation: confetti-fall 1200ms cubic-bezier(.3,.7,.4,1) forwards;
  border-radius: 2px;
}
@keyframes confetti-fall {
  0%   { transform: translateY(-20vh) rotate(0deg);   opacity: 1; }
  100% { transform: translateY(110vh) rotate(720deg); opacity: 0; }
}

/* ----- buttons with ripple ----- */
.btn {
  display: inline-block;
  background: linear-gradient(180deg, var(--primary) 0%, var(--primary-deep) 100%);
  color: #fff;
  border: none;
  padding: 11px 20px;
  font-size: 14px;
  font-weight: 600;
  font-family: var(--font-display);
  letter-spacing: 0.2px;
  border-radius: 10px;
  cursor: pointer;
  text-decoration: none;
  box-shadow: 0 4px 14px rgba(60, 120, 126, 0.30);
  transition: transform 180ms cubic-bezier(.2,.7,.3,1.2),
              box-shadow 180ms ease,
              background 200ms ease;
  position: relative;
  overflow: hidden;
}
.btn:hover {
  transform: translateY(-2px);
  box-shadow: 0 8px 22px rgba(60, 120, 126, 0.40);
}
.btn:active { transform: translateY(0); }
.btn::after {
  content: "";
  position: absolute;
  width: 6px; height: 6px;
  background: rgba(255,255,255,0.55);
  border-radius: 50%;
  top: var(--y, 50%); left: var(--x, 50%);
  transform: translate(-50%, -50%) scale(0);
  pointer-events: none;
}
.btn.ripple::after { animation: ripple 600ms ease-out; }
@keyframes ripple {
  0%   { transform: translate(-50%, -50%) scale(0);  opacity: 1; }
  100% { transform: translate(-50%, -50%) scale(60); opacity: 0; }
}

.btn.ghost {
  background: transparent;
  color: var(--primary-deep);
  border: 2px solid var(--primary);
  box-shadow: none;
}
.btn.ghost:hover {
  background: var(--primary);
  color: #fff;
}

/* ----- lesson navigation ----- */
.lesson-nav {
  display: flex;
  justify-content: space-between;
  gap: 10px;
  margin-top: 40px;
  padding-top: 20px;
  border-top: 1px solid var(--line);
}

/* ----- login overlay ----- */
.login-overlay {
  position: fixed;
  inset: 0;
  background:
    radial-gradient(circle at 25% 25%, rgba(174,197,235,0.55), transparent 55%),
    radial-gradient(circle at 75% 75%, rgba(208,205,148,0.45), transparent 55%),
    var(--bg);
  display: grid;
  place-items: center;
  z-index: 1000;
  animation: fadeIn 320ms ease both;
}
@keyframes fadeIn { from { opacity: 0; } to { opacity: 1; } }
.login-card {
  background: #fff;
  border-radius: 18px;
  padding: 34px 32px;
  box-shadow: 0 24px 60px rgba(40, 60, 65, 0.18);
  width: min(380px, 92vw);
  text-align: center;
  animation: popIn 440ms cubic-bezier(.2,.7,.3,1.4) both;
  border: 1px solid var(--line);
}
@keyframes popIn {
  from { opacity: 0; transform: scale(.92); }
  to   { opacity: 1; transform: scale(1); }
}
.login-card h2 {
  margin: 0 0 4px;
  color: var(--primary-deep);
}
.login-card p { color: var(--muted); margin-bottom: 18px; }
.login-card input {
  width: 100%;
  padding: 13px 14px;
  border: 2px solid var(--line);
  border-radius: 10px;
  font-size: 15px;
  font-family: inherit;
  outline: none;
  transition: border-color 200ms ease, box-shadow 200ms ease;
}
.login-card input:focus {
  border-color: var(--primary);
  box-shadow: 0 0 0 4px rgba(60, 120, 126, 0.14);
}
.login-card .err {
  color: var(--accent);
  font-size: 13px;
  height: 18px;
  margin: 8px 0 4px;
  font-weight: 600;
}
.login-card .btn { width: 100%; margin-top: 6px; }

/* ----- diagrams ----- */
.diagram {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 16px;
  margin: 16px 0;
}
.diagram svg { display: block; max-width: 100%; height: auto; margin: 0 auto; }

/* ----- block ↔ code side-by-side ----- */
.blocks-compare {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
  margin: 16px 0;
}
@media (max-width: 560px) { .blocks-compare { grid-template-columns: 1fr; } }

.block-side, .code-side {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 12px;
  position: relative;
}
.block-side {
  background: linear-gradient(180deg, #F4F7FB 0%, #E6EEF7 100%);
  border-color: var(--sky);
}
.block-side .label, .code-side .label {
  position: absolute;
  top: -10px; left: 12px;
  background: var(--card);
  padding: 0 8px;
  font-family: var(--font-display);
  font-size: 11px;
  letter-spacing: 1.2px;
  text-transform: uppercase;
  color: var(--muted);
  font-weight: 600;
}
.code-side pre { margin: 6px 0 0; }

/* fake "block" tile look */
.fake-block {
  background: linear-gradient(180deg, var(--primary-soft) 0%, var(--primary) 100%);
  color: #fff;
  border-radius: 6px;
  padding: 10px 12px;
  margin: 6px 0;
  font-size: 13px;
  font-weight: 500;
  box-shadow: 0 2px 4px rgba(40,60,65,0.18);
  font-family: var(--font-display);
}
.fake-block.control { background: linear-gradient(180deg, #E0A878 0%, #B07842 100%); }
.fake-block.sense   { background: linear-gradient(180deg, var(--sky-deep) 0%, #5A88B8 100%); }
.fake-block.loop    { background: linear-gradient(180deg, var(--sage-deep) 0%, #837F50 100%); }

/* ----- find the bug exercises ----- */
.bug-section {
  background: linear-gradient(180deg, #F8F2E8 0%, #F0E8D8 100%);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 20px 22px;
  margin: 28px 0;
  position: relative;
  overflow: hidden;
}
.bug-section::before {
  content: "";
  position: absolute;
  top: 0; left: 0; right: 0;
  height: 4px;
  background: linear-gradient(90deg, var(--accent), var(--sage-deep));
}
.bug-section h2 {
  margin-top: 0;
  color: var(--accent);
}
.bug-problem {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 10px;
  padding: 14px 16px;
  margin: 14px 0;
  transition: border-color 200ms ease, box-shadow 200ms ease;
}
.bug-problem:hover {
  border-color: var(--accent);
  box-shadow: 0 6px 18px rgba(104, 80, 68, 0.10);
}
.bug-problem .problem-label {
  font-family: var(--font-display);
  font-size: 11px;
  letter-spacing: 1.4px;
  text-transform: uppercase;
  color: var(--accent);
  font-weight: 700;
  margin-bottom: 6px;
}
.bug-problem .prompt {
  font-family: var(--font-display);
  font-weight: 600;
  margin-bottom: 8px;
  color: var(--ink);
}
.bug-problem pre {
  margin: 8px 0 4px;
}
.bug-problem .hint {
  font-size: 12.5px;
  color: var(--muted);
  margin-top: 8px;
  font-style: italic;
}
.bug-section .answer-ref {
  margin-top: 16px;
  padding: 10px 14px;
  background: rgba(174, 197, 235, 0.30);
  border-radius: 8px;
  font-size: 13px;
  color: var(--ink-soft);
  font-family: var(--font-display);
}

/* ----- open-ended coding challenge ----- */
.challenge {
  background: linear-gradient(180deg, #EAF0EE 0%, #DDE7E6 100%);
  border: 1px solid var(--primary-soft);
  border-radius: var(--radius);
  padding: 22px 24px;
  margin: 28px 0;
  position: relative;
  overflow: hidden;
}
.challenge::before {
  content: "";
  position: absolute;
  top: 0; left: 0; right: 0;
  height: 4px;
  background: linear-gradient(90deg, var(--primary), var(--sky-deep));
}
.challenge .challenge-label {
  font-family: var(--font-display);
  font-size: 11px;
  letter-spacing: 1.4px;
  text-transform: uppercase;
  color: var(--primary-deep);
  font-weight: 700;
  margin-bottom: 6px;
}
.challenge h2 {
  margin: 0 0 6px;
  color: var(--primary-deep);
}
.challenge .prompt {
  font-size: 15px;
  margin: 8px 0 6px;
  color: var(--ink);
}
.challenge ul {
  margin: 8px 0 4px 18px;
  padding: 0;
  font-size: 14px;
  color: var(--ink-soft);
}
.challenge ul li { margin: 2px 0; }
.challenge .no-solution {
  font-family: var(--font-display);
  font-size: 12px;
  color: var(--muted);
  margin-top: 12px;
  letter-spacing: 0.4px;
  font-style: italic;
}

/* ----- badges ----- */
.badge {
  display: inline-block;
  font-family: var(--font-display);
  font-size: 11px;
  font-weight: 600;
  letter-spacing: 1px;
  padding: 4px 10px;
  border-radius: 999px;
  background: rgba(60, 120, 126, 0.12);
  color: var(--primary-deep);
  margin-right: 4px;
  text-transform: uppercase;
}
.badge.gold {
  background: rgba(208, 205, 148, 0.45);
  color: #6B6730;
}
.badge.sky {
  background: rgba(174, 197, 235, 0.45);
  color: #2E5A8C;
}

/* ----- scroll-reveal ----- */
.reveal {
  opacity: 0;
  transform: translateY(14px);
  transition: opacity 600ms ease, transform 600ms cubic-bezier(.2,.7,.3,1);
}
.reveal.in {
  opacity: 1;
  transform: translateY(0);
}

/* ----- mark complete button (animated check) ----- */
.complete-row {
  text-align: center;
  margin-top: 28px;
}
.complete-row .btn {
  min-width: 220px;
  position: relative;
}

/* ----- very narrow ----- */
@media (max-width: 420px) {
  .container { padding: 20px 16px 72px; }
  h1 { font-size: 26px; }
  .topbar nav a { font-size: 13px; padding: 4px 5px; }
}

/* respect reduced motion */
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.001ms !important;
    transition-duration: 0.001ms !important;
  }
}

/* ============================================================
   DARK MODE  (subtle dark grey)
   Activated by data-theme="dark" on the <html> element.
   ============================================================ */
:root[data-theme="dark"] {
  --bg:            #26292B;
  --bg-soft:       #31363A;
  --bg-cool:       #2B3032;
  --card:          #2F3335;
  --primary:       #5FA8AE;
  --primary-deep:  #8AC6CC;
  --primary-soft:  #4C8288;
  --accent:        #E0B49B;
  --sage:          #C7C48C;
  --sage-deep:     #9A9560;
  --sky:           #8FB0DC;
  --sky-deep:      #A9C4E8;
  --ink:           #E9E6DF;
  --ink-soft:      #C0BBB2;
  --muted:         #918B81;
  --line:          #41464A;
  --code-bg:       #1B1E1F;
  --code-ink:      #DCE9EB;
  --shadow:        0 8px 24px rgba(0, 0, 0, 0.35);
  --shadow-lg:     0 20px 50px rgba(0, 0, 0, 0.45);
  --shadow-tilt:   0 18px 36px rgba(0, 0, 0, 0.50);
}

[data-theme="dark"] body {
  background:
    radial-gradient(circle at 8% 4%,  #2E3437 0%, transparent 40%),
    radial-gradient(circle at 92% 96%, #303634 0%, transparent 42%),
    var(--bg);
}
[data-theme="dark"] .card { border-color: #3A3F41; }
[data-theme="dark"] .lesson-card {
  background: linear-gradient(180deg, #2F3335 0%, #292D2F 100%);
  border-color: #3C4143;
}
[data-theme="dark"] .quiz {
  background: linear-gradient(180deg, #2E3234 0%, #292D2F 100%);
}
[data-theme="dark"] .bug-section {
  background: linear-gradient(180deg, #2E3234 0%, #2A2E30 100%);
}
[data-theme="dark"] .bug-problem,
[data-theme="dark"] .resource-list li,
[data-theme="dark"] .quiz-option {
  background: #2C3032;
  color: var(--ink);
}
[data-theme="dark"] .challenge {
  background: linear-gradient(180deg, #2C3335 0%, #28302F 100%);
}
[data-theme="dark"] .analogy {
  background: linear-gradient(135deg, #33383A 0%, #2D3133 100%);
}
[data-theme="dark"] .callout.warn { background: #38302C; }
[data-theme="dark"] .callout.tip  { background: #353629; }
[data-theme="dark"] .diagram { background: #2C3032; }
[data-theme="dark"] .block-side {
  background: linear-gradient(180deg, #2C3236 0%, #283034 100%);
  border-color: #3D4346;
}
[data-theme="dark"] .code-side { background: var(--card); }
[data-theme="dark"] code { background: rgba(95, 168, 174, 0.18); }
[data-theme="dark"] .login-card { background: #2F3335; }
[data-theme="dark"] .login-card input { background: #262A2C; color: var(--ink); }
[data-theme="dark"] .login-overlay {
  background:
    radial-gradient(circle at 25% 25%, rgba(95,168,174,0.15), transparent 55%),
    radial-gradient(circle at 75% 75%, rgba(199,196,140,0.10), transparent 55%),
    var(--bg);
}

/* theme toggle button */
#theme-toggle {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 6px;
  width: 34px;
  height: 32px;
}
#theme-toggle svg { display: block; }

/* subtle byline in the header */
.brand .byline {
  font-family: var(--font-body);
  font-weight: 400;
  font-size: 12px;
  color: var(--muted);
  letter-spacing: 0;
}
.brand .byline a {
  color: inherit;
  text-decoration: none;
  transition: color 160ms ease;
}
.brand .byline a:hover { color: var(--primary-deep); text-decoration: underline; }
#site-footer a { color: inherit; text-decoration: none; }
#site-footer a:hover { text-decoration: underline; }