:root {
  color-scheme: light;
  --ink: #172033;
  --muted: #64748b;
  --line: #dbe3f0;
  --brand: #4f46e5;
  --brand-dark: #3730a3;
  --gold: #f59e0b;
  --success: #15803d;
  --danger: #b91c1c;
}

* { box-sizing: border-box; }

body {
  min-height: 100vh;
  margin: 0;
  background:
    radial-gradient(circle at 15% 15%, rgba(99, 102, 241, .12), transparent 30rem),
    #f8fafc;
  color: var(--ink);
  font-family: Inter, system-ui, sans-serif;
}

.lab-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  max-width: 1180px;
  margin: auto;
  padding: 1.25rem 1.5rem;
}

.brand {
  display: flex;
  gap: .65rem;
  align-items: center;
  color: var(--ink);
  font-weight: 800;
  text-decoration: none;
}

.brand img { width: 34px; height: 34px; }

.founding-link {
  padding: .65rem .95rem;
  border-radius: 999px;
  background: #eef2ff;
  color: var(--brand-dark);
  font-size: .88rem;
  font-weight: 700;
  text-decoration: none;
}

.lab-shell {
  display: grid;
  grid-template-columns: minmax(270px, .78fr) minmax(0, 1.35fr);
  gap: clamp(1.5rem, 4vw, 4rem);
  max-width: 1180px;
  margin: 2rem auto;
  padding: 0 1.5rem;
}

.lesson-intro {
  align-self: start;
  position: sticky;
  top: 1.5rem;
}

.eyebrow {
  margin: 0 0 .6rem;
  color: var(--brand);
  font-size: .78rem;
  font-weight: 800;
  letter-spacing: .12em;
  text-transform: uppercase;
}

h1 {
  margin: 0;
  font-size: clamp(2rem, 4vw, 3.25rem);
  line-height: 1.06;
  letter-spacing: -.04em;
}

.lesson-promise {
  color: var(--muted);
  line-height: 1.7;
}

.progress-copy {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  margin-top: 2rem;
  color: var(--muted);
  font-size: .82rem;
  font-weight: 600;
}

.progress-track {
  height: 10px;
  margin-top: .55rem;
  overflow: hidden;
  border-radius: 999px;
  background: #e2e8f0;
}

#progress-bar {
  width: 0;
  height: 100%;
  border-radius: inherit;
  background: linear-gradient(90deg, var(--brand), #8b5cf6);
  transition: width .35s ease;
}

.hud {
  margin-top: 1rem;
  padding: .85rem 1rem;
  border: 1px solid #c7d2fe;
  border-radius: 12px;
  background: #eef2ff;
  color: var(--brand-dark);
  font-size: .86rem;
  font-weight: 700;
}

.method-card {
  margin-top: 1.5rem;
  padding: 1rem 1.1rem;
  border: 1px solid var(--line);
  border-radius: 14px;
  background: rgba(255, 255, 255, .72);
}

.method-card ul {
  display: grid;
  gap: .55rem;
  margin: .8rem 0 0;
  padding-left: 1.1rem;
  color: var(--muted);
  font-size: .88rem;
}

.lesson-stage {
  min-height: 580px;
  padding: clamp(1.4rem, 4vw, 3rem);
  border: 1px solid rgba(203, 213, 225, .9);
  border-radius: 24px;
  background: rgba(255, 255, 255, .94);
  box-shadow: 0 24px 70px rgba(51, 65, 85, .12);
}

.block { animation: enter .3s ease-out; }
.block-kicker { color: var(--brand); font-size: .76rem; font-weight: 800; letter-spacing: .1em; text-transform: uppercase; }
.block h2 { margin: .45rem 0 1rem; font-size: clamp(1.65rem, 3vw, 2.35rem); line-height: 1.15; }
.block p { color: #334155; font-size: 1.04rem; line-height: 1.75; }
.who { color: var(--muted) !important; font-style: italic; }

.answers, .grade { display: grid; gap: .75rem; margin-top: 1.5rem; }

.block button,
.completion-card a {
  width: 100%;
  margin-top: .8rem;
  padding: .9rem 1rem;
  border: 1px solid #cbd5e1;
  border-radius: 12px;
  background: #fff;
  color: var(--ink);
  font: 600 1rem Inter, sans-serif;
  text-align: left;
  cursor: pointer;
  transition: border-color .15s, transform .15s, background .15s;
}

.block button:hover { border-color: var(--brand); transform: translateY(-1px); }
.block button.primary { background: var(--brand); border-color: var(--brand); color: #fff; text-align: center; }
.block button.ok { background: #dcfce7; border-color: #22c55e; color: #166534; }
.block button.bad { background: #fee2e2; border-color: #ef4444; color: #991b1b; }
.block button:disabled { cursor: default; transform: none; }

textarea {
  width: 100%;
  min-height: 220px;
  margin-top: 1rem;
  padding: 1rem;
  border: 1px solid #94a3b8;
  border-radius: 12px;
  background: #111827;
  color: #e5e7eb;
  font: 500 .9rem/1.6 "JetBrains Mono", monospace;
  resize: vertical;
}

.feedback {
  min-height: 1.5rem;
  font-weight: 700;
}

.timer { color: var(--danger) !important; font-weight: 800; }

.completion-card {
  display: grid;
  place-items: center;
  min-height: 480px;
  text-align: center;
}

.completion-card .celebration { font-size: 4rem; }
.completion-card a { display: inline-block; width: auto; padding: .9rem 1.25rem; background: var(--brand); color: #fff; text-decoration: none; }

#flash {
  position: fixed;
  top: 1rem;
  left: 50%;
  z-index: 20;
  transform: translateX(-50%);
  padding: .7rem 1.2rem;
  border-radius: 999px;
  background: var(--ink);
  color: #fff;
  font-weight: 700;
  box-shadow: 0 10px 30px rgba(0, 0, 0, .22);
}

footer {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  max-width: 1180px;
  margin: 2rem auto 0;
  padding: 1.5rem;
  color: var(--muted);
  font-size: .85rem;
}

footer a { color: var(--brand); font-weight: 700; text-decoration: none; }

@keyframes enter {
  from { opacity: 0; transform: translateY(8px); }
  to { opacity: 1; transform: none; }
}

@media (max-width: 800px) {
  .lab-shell { grid-template-columns: 1fr; margin-top: .5rem; }
  .lesson-intro { position: static; }
  .method-card { display: none; }
  .lesson-stage { min-height: 480px; }
}

@media (max-width: 520px) {
  .lab-header { padding: 1rem; }
  .brand span { font-size: .95rem; }
  .founding-link { font-size: .75rem; }
  .lab-shell { padding: 0 1rem; }
  .lesson-stage { padding: 1.25rem; border-radius: 18px; }
  footer { flex-direction: column; padding: 1rem; }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { scroll-behavior: auto !important; animation: none !important; transition: none !important; }
}