/* Notebook palette: ballpoint blue, highlighter yellow, ink navy on cool paper. */
:root {
  --paper: #F6F8FB;
  --surface: #FFFFFF;
  --ink: #16213A;
  --ink-soft: #4A5670;
  --line: #D5DBE6;
  --blue: #2447C8;
  --on-blue: #FFFFFF;
  --mark: #FFE14D;
  --on-mark: #16213A;
  --good: #17794F;
  --bad: #B3364A;
  --serif: "Iowan Old Style", "Palatino Linotype", Palatino, "Book Antiqua", Georgia, serif;
  --sans: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --gutter: clamp(16px, 4vw, 40px);
}

@media (prefers-color-scheme: dark) {
  :root {
    --paper: #0E1526;
    --surface: #16203A;
    --ink: #E8EDF8;
    --ink-soft: #A9B4CC;
    --line: #2B3858;
    --blue: #8FA8FF;
    --on-blue: #0E1526;
    --good: #5FD39B;
    --bad: #FF8A9B;
  }
}

*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font: 1.0625rem/1.65 var(--sans);
}

a { color: var(--blue); text-underline-offset: 0.18em; }
a:hover { text-decoration-thickness: 2px; }
:focus-visible { outline: 3px solid var(--blue); outline-offset: 3px; border-radius: 4px; }

.skip {
  position: absolute; left: -999px; top: 0; z-index: 10;
  background: var(--surface); color: var(--ink); padding: 0.6rem 1rem;
}
.skip:focus { left: var(--gutter); top: 0.5rem; }

/* header */
.site-header {
  display: flex; flex-wrap: wrap; align-items: baseline; justify-content: space-between;
  gap: 0.5rem 1.5rem; max-width: 72rem; margin: 0 auto; padding: 1.1rem var(--gutter);
}
.brand { font: 700 1.3rem/1.2 var(--serif); color: var(--ink); text-decoration: none; }
.site-header nav { display: flex; flex-wrap: wrap; gap: 0.25rem 1.5rem; }
.site-header nav a {
  color: var(--ink-soft); text-decoration: none; padding: 0.25rem 0;
  border-bottom: 2px solid transparent;
}
.site-header nav a:hover { color: var(--ink); border-bottom-color: var(--line); }
.site-header nav a[aria-current="page"] { color: var(--ink); border-bottom-color: var(--blue); }

/* type */
h1, h2, h3 { font-family: var(--serif); color: var(--ink); text-wrap: balance; }
h1 {
  font-size: clamp(2.1rem, 5.2vw, 3.5rem); line-height: 1.08; letter-spacing: -0.015em;
  margin: 0 0 1rem; font-weight: 700;
}
h2 { font-size: clamp(1.5rem, 3vw, 1.9rem); line-height: 1.2; margin: 2.75rem 0 0.75rem; }
h3 { font-size: 1.2rem; line-height: 1.3; margin: 0 0 0.25rem; }
p { margin: 0 0 1rem; }
.lede { font-size: 1.2rem; line-height: 1.55; color: var(--ink-soft); max-width: 34rem; }
.note { color: var(--ink-soft); font-size: 0.95rem; max-width: 34rem; }
.status { font-weight: 600; }

.btn {
  display: inline-block; background: var(--blue); color: var(--on-blue);
  padding: 0.75rem 1.25rem; border-radius: 10px; font: 600 1rem/1.2 var(--sans);
  text-decoration: none; border: 0; cursor: pointer;
}
.btn:hover { text-decoration: underline; }
.btn.quiet {
  background: transparent; color: var(--blue); border: 2px solid var(--blue); padding: 0.6rem 1.1rem;
}

/* home hero */
.hero {
  display: grid; gap: 2.5rem; max-width: 72rem; margin: 0 auto;
  padding: clamp(1.5rem, 5vw, 4.5rem) var(--gutter) clamp(2.5rem, 6vw, 5rem);
}
@media (min-width: 56rem) {
  .hero { grid-template-columns: minmax(0, 1.05fr) minmax(0, 0.95fr); align-items: center; gap: 4rem; }
}

/* the sample question: the one memorable element */
.demo {
  background: var(--surface); border: 2px solid var(--ink); border-radius: 16px;
  padding: clamp(1.1rem, 3vw, 1.75rem); box-shadow: 6px 6px 0 var(--blue); max-width: 34rem;
}
@media (max-width: 40rem) { .demo { box-shadow: 4px 4px 0 var(--blue); } }
.demo h2 { font-size: 1.1rem; margin: 0 0 0.9rem; color: var(--ink-soft); font-family: var(--sans); font-weight: 600; }
.sentence { font: 1.35rem/1.55 var(--serif); margin: 0 0 1.25rem; }
.blank {
  display: inline-block; min-width: 7ch; border-bottom: 2px solid var(--ink);
  vertical-align: baseline; text-align: center;
}
.blank.filled {
  border-bottom: 0; padding: 0 0.25em; color: var(--on-mark); font-weight: 700;
  background: linear-gradient(var(--mark), var(--mark)) left center / 100% 100% no-repeat;
  animation: swipe 0.45s ease-out;
}
@keyframes swipe { from { background-size: 0 100%; } to { background-size: 100% 100%; } }
@media (prefers-reduced-motion: reduce) { .blank.filled { animation: none; } }

.choices { display: grid; gap: 0.6rem; grid-template-columns: 1fr 1fr; margin: 0 0 1rem; }
@media (max-width: 22rem) { .choices { grid-template-columns: 1fr; } }
.choice {
  font: 1rem/1.3 var(--sans); color: var(--ink); text-align: left; background: var(--surface);
  border: 2px solid var(--line); border-radius: 10px; padding: 0.7rem 0.9rem; cursor: pointer;
}
.choice:hover:not(:disabled) { border-color: var(--ink); }
.choice:disabled { color: var(--ink); cursor: default; }
.choice.correct { border-color: var(--good); background: color-mix(in srgb, var(--good) 16%, var(--surface)); }
.choice.wrong { border-color: var(--bad); background: color-mix(in srgb, var(--bad) 14%, var(--surface)); }
.feedback { min-height: 3.4em; margin: 0 0 0.75rem; font-size: 0.98rem; }
.demo-foot { display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: 0.75rem; }
.demo-count { color: var(--ink-soft); font-size: 0.9rem; margin: 0; }

/* sections */
.band { border-top: 1px solid var(--line); }
.band-inner { max-width: 72rem; margin: 0 auto; padding: clamp(2rem, 5vw, 4rem) var(--gutter); }
.band-inner h2:first-child, .reading > h2:first-child { margin-top: 0; }
.reading { max-width: 44rem; }

.steps { list-style: none; margin: 1.5rem 0 0; padding: 0; counter-reset: step; max-width: 44rem; }
.steps li {
  counter-increment: step; display: grid; grid-template-columns: 3.25rem 1fr; gap: 0 0.5rem;
  padding: 1rem 0; border-top: 1px solid var(--line);
}
.steps li::before {
  content: counter(step); font: 700 2.1rem/1 var(--serif); color: var(--blue);
}
.steps p { margin: 0; color: var(--ink-soft); }

/* text pages */
.prose { max-width: 44rem; margin: 0 auto; padding: clamp(1.5rem, 5vw, 3.5rem) var(--gutter) 4rem; }
.prose h1 { font-size: clamp(2rem, 4.6vw, 2.9rem); }
.prose .meta { color: var(--ink-soft); font-size: 0.95rem; margin-top: -0.5rem; }
.prose ul { padding-left: 1.25rem; }
.prose li { margin-bottom: 0.4rem; }
.features dt { font-weight: 700; margin-top: 1.25rem; }
.features dd { margin: 0.1rem 0 0; color: var(--ink-soft); }

details { border-top: 1px solid var(--line); padding: 0.85rem 0; }
details:last-of-type { border-bottom: 1px solid var(--line); }
summary { cursor: pointer; font-weight: 600; }
details > :not(summary) { margin: 0.6rem 0 0; color: var(--ink-soft); }

/* footer */
.site-footer {
  border-top: 1px solid var(--line); max-width: 72rem; margin: 0 auto;
  padding: 2rem var(--gutter) 3rem;
}
.footer-row { display: flex; flex-wrap: wrap; justify-content: space-between; gap: 1.5rem; margin-bottom: 1.25rem; }
.footer-company { margin: 0; overflow-wrap: anywhere; }
.footer-links { list-style: none; margin: 0; padding: 0; display: flex; flex-wrap: wrap; gap: 0.4rem 1.5rem; align-content: flex-start; }
.fine { font-size: 0.85rem; color: var(--ink-soft); max-width: 52rem; margin: 0 0 0.5rem; }