/* LearnVestory — Stage 00 scaffold. Hand-written CSS, no framework, no CDN. */
:root {
  --bg: #f8fafc;
  --surface: #ffffff;
  --ink: #0f172a;
  --muted: #475569;
  --brand: #0f766e;
  --brand-ink: #ffffff;
  --accent: #14b8a6;
  --warn-bg: #fef3c7;
  --warn-ink: #92400e;
  --border: #e2e8f0;
  --radius: 14px;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family:
    system-ui,
    -apple-system,
    "Segoe UI",
    Roboto,
    "Helvetica Neue",
    Arial,
    sans-serif;
  background: var(--bg);
  color: var(--ink);
  line-height: 1.55;
}

.dev-banner {
  background: var(--warn-bg);
  color: var(--warn-ink);
  text-align: center;
  padding: 0.55rem 1rem;
  font-size: 0.9rem;
  font-weight: 600;
}

.hero {
  max-width: 46rem;
  margin: 0 auto;
  padding: 3.5rem 1.25rem 2rem;
  text-align: center;
}

.hero h1 {
  margin: 0;
  font-size: clamp(2.2rem, 6vw, 3.4rem);
  letter-spacing: -0.02em;
  background: linear-gradient(90deg, var(--brand), var(--accent));
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
}

.tagline {
  margin: 0.4rem 0 0;
  font-size: clamp(1.05rem, 2.8vw, 1.3rem);
  font-weight: 600;
  color: var(--brand);
}

.lede {
  margin: 0.9rem auto 0;
  max-width: 34rem;
  color: var(--muted);
  font-size: 1.05rem;
}

main {
  max-width: 60rem;
  margin: 0 auto;
  padding: 0 1.25rem 3rem;
}

.cards {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(min(15rem, 100%), 1fr));
  gap: 1rem;
}

.card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem 1.25rem 1rem;
  display: flex;
  flex-direction: column;
  gap: 0.4rem;
  min-width: 0;
}

.card h2 {
  margin: 0;
  font-size: 1.15rem;
  color: var(--brand);
}

.card p {
  margin: 0;
  color: var(--muted);
  font-size: 0.95rem;
  flex: 1;
}

.badge {
  align-self: flex-start;
  font-size: 0.72rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  color: var(--brand);
  background: #ccfbf1;
  border-radius: 999px;
  padding: 0.15rem 0.6rem;
}

.calc {
  margin-top: 2.5rem;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.5rem 1.25rem;
}

.calc h2 {
  margin: 0 0 0.25rem;
  font-size: 1.3rem;
}

.calc-note {
  margin: 0 0 1.1rem;
  color: var(--muted);
  font-size: 0.95rem;
}

#dividend-form {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(min(13rem, 100%), 1fr));
  gap: 0.9rem;
  align-items: end;
}

.field {
  display: flex;
  flex-direction: column;
  gap: 0.3rem;
  min-width: 0;
}

.field label {
  font-size: 0.88rem;
  font-weight: 600;
}

.field input {
  font: inherit;
  padding: 0.6rem 0.75rem;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: var(--bg);
  min-width: 0;
}

.field input:focus {
  outline: 2px solid var(--accent);
  outline-offset: 1px;
}

button {
  font: inherit;
  font-weight: 700;
  color: var(--brand-ink);
  background: var(--brand);
  border: 0;
  border-radius: 10px;
  padding: 0.65rem 1.4rem;
  cursor: pointer;
  min-height: 44px;
}

button:hover {
  background: #0d655e;
}

.result {
  margin: 1rem 0 0;
  min-height: 1.5rem;
  font-size: 1.08rem;
  font-weight: 700;
  color: var(--brand);
}

.result.error {
  color: #b91c1c;
}

.formula {
  margin-top: 0.75rem;
  color: var(--muted);
  font-size: 0.92rem;
}

.formula summary {
  cursor: pointer;
  font-weight: 600;
}

footer {
  border-top: 1px solid var(--border);
  max-width: 60rem;
  margin: 0 auto;
  padding: 1.5rem 1.25rem 2.5rem;
  color: var(--muted);
  font-size: 0.88rem;
}

footer p {
  margin: 0 0 0.6rem;
}

/* ---- Lesson pages (Stage 01) ---- */

main.lesson {
  max-width: 44rem;
  margin: 0 auto;
  padding: 1.25rem 1.25rem 3rem;
}

.crumbs {
  margin: 0 0 1.25rem;
}

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

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

.lesson-head h1 {
  margin: 0.1rem 0 0.3rem;
  font-size: clamp(1.7rem, 5vw, 2.4rem);
  letter-spacing: -0.02em;
}

.kicker {
  margin: 0;
  text-transform: uppercase;
  letter-spacing: 0.07em;
  font-size: 0.78rem;
  font-weight: 700;
  color: var(--accent);
}

.lesson-meta {
  margin: 0.2rem 0 0;
  color: var(--muted);
  font-size: 0.92rem;
}

main.lesson section {
  margin-top: 2rem;
}

main.lesson h2 {
  font-size: 1.25rem;
  margin: 0 0 0.5rem;
  color: var(--brand);
}

main.lesson a {
  color: var(--brand);
}

.formula-box {
  background: #f0fdfa;
  border: 1px solid #99f6e4;
  border-radius: 10px;
  padding: 0.8rem 1rem;
  font-weight: 700;
  text-align: center;
  overflow-wrap: anywhere;
}

.aside {
  border-left: 4px solid var(--accent);
  background: #f8fafc;
  padding: 0.6rem 0.9rem;
  border-radius: 0 10px 10px 0;
  color: var(--ink);
}

.quiz-wrap {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem;
}

.quiz-q {
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 0.9rem 1rem;
  margin: 0 0 0.9rem;
}

.quiz-q legend {
  font-weight: 700;
  padding: 0 0.4rem;
}

.quiz-opt {
  display: flex;
  gap: 0.5rem;
  align-items: baseline;
  padding: 0.3rem 0;
  cursor: pointer;
}

.quiz-opt input {
  accent-color: var(--brand);
  width: 1.05rem;
  height: 1.05rem;
}

.quiz-fb {
  margin: 0.5rem 0 0;
  min-height: 1.2rem;
  font-size: 0.93rem;
  font-weight: 600;
}

.quiz-fb.good {
  color: #047857;
}

.quiz-fb.bad {
  color: #b91c1c;
}

.lesson-foot {
  border: 0;
  max-width: none;
  padding: 1.75rem 0 0;
}

.badge-link {
  text-decoration: none;
}

.badge-link:hover {
  background: #99f6e4;
}