:root {
  color-scheme: light;
  --ink: #17221d;
  --muted: #59675f;
  --paper: #f5f2e9;
  --surface: #fffdf7;
  --forest: #174b3a;
  --forest-dark: #0c3528;
  --lime: #d8ed83;
  --line: #d8d8ca;
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, sans-serif;
}
* { box-sizing: border-box; }
body { margin: 0; color: var(--ink); background: var(--paper); line-height: 1.55; }
a { color: var(--forest); text-underline-offset: .18em; }
.prototype-banner {
  display: flex;
  justify-content: center;
  gap: .65rem;
  padding: .55rem 1rem;
  color: #fff;
  background: var(--forest-dark);
  font-size: .82rem;
}
.site-header, main, footer {
  width: min(70rem, calc(100% - 2rem));
  margin-inline: auto;
}
.site-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding-block: 1.35rem;
  border-bottom: 1px solid var(--line);
}
.wordmark {
  color: var(--ink);
  font-family: Georgia, serif;
  font-size: 1.55rem;
  font-weight: 700;
  text-decoration: none;
  letter-spacing: -.04em;
}
.mode {
  padding: .35rem .65rem;
  border: 1px solid var(--line);
  border-radius: 999px;
  color: var(--muted);
  font-size: .78rem;
}
main { min-height: calc(100vh - 12rem); padding-block: clamp(2.4rem, 7vw, 5.8rem); }
.hero {
  display: grid;
  grid-template-columns: 1.4fr .8fr;
  gap: 2rem;
  align-items: end;
  margin-bottom: 3rem;
}
h1, h2, p { margin-top: 0; }
h1, h2 { line-height: 1.08; letter-spacing: -.035em; }
h1 {
  max-width: 12ch;
  margin-bottom: 1rem;
  font-family: Georgia, serif;
  font-size: clamp(3rem, 8vw, 6.2rem);
  font-weight: 500;
}
h2 { font-size: 1.45rem; }
.lead { max-width: 42rem; color: var(--muted); font-size: clamp(1.05rem, 2.4vw, 1.35rem); }
.eyebrow {
  margin-bottom: .65rem;
  color: var(--forest);
  font-size: .75rem;
  font-weight: 800;
  letter-spacing: .12em;
  text-transform: uppercase;
}
.privacy-card {
  display: flex;
  gap: .8rem;
  padding: 1.25rem;
  border: 1px solid #bfd19d;
  border-radius: 1rem;
  background: #eff6d9;
  box-shadow: 0 .8rem 2rem rgba(23, 75, 58, .08);
}
.privacy-card p { margin: .25rem 0 0; color: var(--muted); font-size: .9rem; }
.status-dot {
  flex: 0 0 auto;
  width: .7rem;
  height: .7rem;
  margin-top: .42rem;
  border-radius: 50%;
  background: #4f821e;
  box-shadow: 0 0 0 .25rem rgba(79, 130, 30, .12);
}
.exercise-grid { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 1.2rem; }
.exercise-card, .practice-panel {
  border: 1px solid var(--line);
  border-radius: 1.15rem;
  background: var(--surface);
  box-shadow: 0 1rem 2.5rem rgba(40, 50, 43, .06);
}
.exercise-card {
  display: flex;
  min-height: 18rem;
  flex-direction: column;
  padding: clamp(1.5rem, 4vw, 2.2rem);
}
.exercise-card p:not(.eyebrow) { color: var(--muted); }
.button {
  align-self: flex-start;
  margin-top: auto;
  padding: .7rem 1rem;
  border-radius: .55rem;
  color: #fff;
  background: var(--forest);
  font-weight: 750;
  text-decoration: none;
}
.button:hover, button:hover { background: var(--forest-dark); }
.boundary {
  max-width: 44rem;
  margin-top: 3rem;
  padding-top: 1.4rem;
  border-top: 1px solid var(--line);
  color: var(--muted);
}
.boundary h2 { color: var(--ink); }
nav { margin-bottom: 1.2rem; }
.practice-panel { max-width: 49rem; padding: clamp(1.5rem, 6vw, 3.5rem); }
.practice-panel h1 { max-width: 15ch; font-size: clamp(2.5rem, 7vw, 4.8rem); }
.problem-statement {
  margin: 2rem 0;
  padding: 1.25rem 1.4rem;
  border-left: .3rem solid var(--lime);
  background: #f1f4e5;
  font-size: 1.08rem;
}
.problem-statement p:last-child { margin-bottom: 0; }
.formula {
  overflow-wrap: anywhere;
  font-family: Georgia, serif;
  font-size: clamp(1.25rem, 4vw, 1.8rem);
}
form { margin-top: 2rem; }
label { display: block; margin-bottom: .45rem; font-weight: 750; }
input {
  width: 100%;
  padding: .9rem 1rem;
  border: 1px solid #a6afa8;
  border-radius: .55rem;
  color: var(--ink);
  background: #fff;
  font: inherit;
}
input:focus { outline: .2rem solid rgba(23, 75, 58, .2); border-color: var(--forest); }
.notation-help, .ephemeral-note { color: var(--muted); font-size: .88rem; }
.notation-help { margin: .55rem 0 1rem; }
button {
  padding: .75rem 1.1rem;
  border: 0;
  border-radius: .55rem;
  color: #fff;
  background: var(--forest);
  font: inherit;
  font-weight: 750;
  cursor: pointer;
}
.feedback { margin-top: 1.2rem; padding: .9rem 1rem; border-radius: .55rem; font-weight: 750; }
.feedback.correct { color: #18430d; background: #e0f2cf; }
.feedback.incorrect, .feedback.error { color: #6a3518; background: #f8e8d7; }
.ephemeral-note { margin: 1.4rem 0 0; padding-top: 1.2rem; border-top: 1px solid var(--line); }
footer {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  padding-block: 1.4rem 2rem;
  border-top: 1px solid var(--line);
  color: var(--muted);
  font-size: .82rem;
}
@media (max-width: 43rem) {
  .prototype-banner { display: block; text-align: center; }
  .prototype-banner span { display: block; }
  .hero, .exercise-grid { grid-template-columns: 1fr; }
  .site-header, footer { align-items: flex-start; }
  footer { flex-direction: column; }
}