/* SAT Formula Lab — shared styles */
:root {
  --ink: #101322;
  --ink-soft: #46506b;
  --ink-faint: #7a829b;
  --bg: #f7f8fc;
  --surface: #ffffff;
  --line: #e4e7f0;
  --brand: #3532e0;
  --brand-deep: #211fa8;
  --brand-soft: #eeedff;
  --given: #067d55;
  --given-bg: #e7f7ef;
  --memo: #b4530a;
  --memo-bg: #fdf0e0;
  --core: #3532e0;
  --supp: #6b7390;
  --ok: #0a7a45;
  --bad: #c03434;
  --radius: 16px;
  --shadow: 0 1px 2px rgba(16, 19, 34, 0.05), 0 8px 24px rgba(16, 19, 34, 0.07);
  --maxw: 1120px;
  --font: -apple-system, BlinkMacSystemFont, "SF Pro Text", "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --display: "Space Grotesk", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --mono: ui-monospace, "SF Mono", SFMono-Regular, Menlo, Consolas, monospace;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  font-family: var(--font);
  color: var(--ink);
  /* faint graph-paper grid: on-theme texture for a calculator-era study tool */
  background-color: var(--bg);
  background-image:
    linear-gradient(rgba(53, 50, 224, 0.035) 1px, transparent 1px),
    linear-gradient(90deg, rgba(53, 50, 224, 0.035) 1px, transparent 1px);
  background-size: 36px 36px;
  line-height: 1.55;
  -webkit-font-smoothing: antialiased;
}
a { color: var(--brand); text-decoration: none; }
a:hover { text-decoration: underline; }
img, svg { max-width: 100%; }
.container { max-width: var(--maxw); margin: 0 auto; padding: 0 20px; }

h1, h2, h3, .logo, .kicker, .strip .s-num, .result-hero .big {
  font-family: var(--display);
}
h1, h2, h3 { text-wrap: balance; }
.score, .q-domain, .result-hero .big { font-variant-numeric: tabular-nums; }

/* focus + motion feedback */
:focus-visible { outline: 2.5px solid var(--brand); outline-offset: 2px; border-radius: 6px; }
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { animation: none !important; transition: none !important; }
}
@keyframes rise {
  from { opacity: 0; transform: translateY(10px); }
  to { opacity: 1; transform: none; }
}

/* ---------- Header / nav ---------- */
.site-head {
  position: sticky; top: 0; z-index: 50;
  background: rgba(255, 255, 255, 0.92);
  backdrop-filter: saturate(180%) blur(12px);
  border-bottom: 1px solid var(--line);
}
.site-head .row {
  display: flex; align-items: center; gap: 20px;
  height: 60px;
}
.logo { display: flex; align-items: baseline; gap: 8px; font-weight: 800; font-size: 18px; color: var(--ink); letter-spacing: -0.02em; }
.logo .fx { color: var(--brand); }
.logo:hover { text-decoration: none; }
.nav-links { display: flex; gap: 4px; margin-left: auto; }
.nav-links a {
  padding: 7px 13px; border-radius: 999px;
  color: var(--ink-soft); font-weight: 600; font-size: 14.5px;
}
.nav-links a:hover { background: var(--brand-soft); color: var(--brand-deep); text-decoration: none; }
.nav-links a.cta {
  background: var(--brand); color: #fff;
}
.nav-links a.cta:hover { background: var(--brand-deep); }
/* short labels kick in below 640px (see media queries) */
.nav-short { display: none; }
/* current-page indicator (pure CSS, driven by body[data-page]) */
body[data-page="formulas"] .nav-links a[href="formulas.html"]:not(.cta),
body[data-page="desmos"] .nav-links a[href="desmos.html"]:not(.cta) {
  background: var(--brand-soft); color: var(--brand-deep);
}
body[data-page="diagnose"] .nav-links a.cta {
  box-shadow: 0 0 0 2px var(--brand-soft), 0 0 0 4px rgba(53, 50, 224, 0.25);
}

/* ---------- Hero ---------- */
.hero { padding: 64px 0 48px; }
.hero .kicker {
  display: inline-flex; align-items: center; gap: 8px;
  font-size: 13px; font-weight: 700; letter-spacing: 0.06em;
  text-transform: uppercase; color: var(--brand);
  background: var(--brand-soft); border-radius: 999px; padding: 6px 14px;
}
.hero h1 {
  font-size: clamp(30px, 5vw, 46px); line-height: 1.12;
  letter-spacing: -0.025em; margin: 18px 0 14px; max-width: 780px;
}
.hero h1 .accent { color: var(--brand); }
.hero p.lede { font-size: 18px; color: var(--ink-soft); max-width: 680px; margin: 0 0 26px; }
.hero-actions { display: flex; flex-wrap: wrap; gap: 12px; }
.btn {
  display: inline-flex; align-items: center; gap: 8px;
  padding: 12px 22px; border-radius: 12px;
  font-weight: 700; font-size: 15.5px; border: 1.5px solid transparent;
  cursor: pointer; transition: transform 0.06s ease, background 0.12s ease;
}
.btn:active { transform: translateY(1px); }
.btn:hover { text-decoration: none; }
.btn-primary { background: var(--brand); color: #fff; }
.btn-primary:hover { background: var(--brand-deep); }
.btn-ghost { background: #fff; color: var(--ink); border-color: var(--line); }
.btn-ghost:hover { border-color: var(--brand); color: var(--brand); }

/* ---------- Badges & chips ---------- */
.badge {
  display: inline-flex; align-items: center; gap: 5px;
  font-size: 11.5px; font-weight: 800; letter-spacing: 0.05em;
  text-transform: uppercase; padding: 3px 9px; border-radius: 999px;
  white-space: nowrap;
}
.badge.given { color: var(--given); background: var(--given-bg); }
.badge.memo { color: var(--memo); background: var(--memo-bg); }
.badge.core { color: var(--core); background: var(--brand-soft); }
.badge.supp { color: var(--supp); background: #eef0f6; }
.badge.bb { color: #fff; background: var(--ok); }

.chips { display: flex; flex-wrap: wrap; gap: 8px; margin: 18px 0 26px; }
.chip {
  padding: 7px 14px; border-radius: 999px; cursor: pointer;
  border: 1.5px solid var(--line); background: #fff;
  font-size: 13.5px; font-weight: 700; color: var(--ink-soft);
}
.chip:hover { border-color: var(--brand); color: var(--brand); }
.chip:active { transform: scale(0.97); }
.chip.on { background: var(--brand); border-color: var(--brand); color: #fff; }

/* ---------- Cards ---------- */
.page-head { padding: 40px 0 6px; }
.page-head h1 { font-size: clamp(26px, 4vw, 36px); letter-spacing: -0.02em; margin: 8px 0 8px; }
.page-head p.sub { color: var(--ink-soft); font-size: 16.5px; max-width: 720px; margin: 0 0 8px; }

.section { margin: 34px 0; }
.section > h2 {
  font-size: 21px; letter-spacing: -0.015em; margin: 0 0 4px;
  display: flex; align-items: center; gap: 10px; flex-wrap: wrap;
}
.section .sec-sub { color: var(--ink-faint); font-size: 14px; margin: 0 0 16px; }

.card-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(min(330px, 100%), 1fr)); gap: 16px; }

.formula-card {
  background: var(--surface); border: 1px solid var(--line);
  border-radius: var(--radius); padding: 18px 18px 14px;
  box-shadow: var(--shadow); display: flex; flex-direction: column; gap: 10px;
  scroll-margin-top: 90px;
  transition: transform 0.18s ease, border-color 0.18s ease, box-shadow 0.18s ease;
}
.formula-card:hover { transform: translateY(-2px); border-color: #c3c2f2; }
#formula-grid { animation: rise 0.5s cubic-bezier(0.2, 0.7, 0.3, 1) both; }
.formula-card .top { display: flex; align-items: flex-start; gap: 10px; }
.formula-card h3 { font-size: 16.5px; margin: 0; flex: 1; letter-spacing: -0.01em; }
.formula-card .badges { display: flex; gap: 6px; flex-wrap: wrap; }
.formula-card .latex {
  background: #f4f5fb; border-radius: 10px; padding: 12px 14px;
  font-size: 17px; overflow-x: auto; text-align: center;
}
.formula-card .when { font-size: 13.5px; color: var(--ink-soft); margin: 0; }
.formula-card details { font-size: 13.5px; color: var(--ink-soft); }
.formula-card details summary { cursor: pointer; font-weight: 700; color: var(--brand); }
.formula-card details .ans { color: var(--ok); font-weight: 700; }
.formula-card .to-tech { font-size: 13px; font-weight: 700; }
.formula-card.targeted { outline: 3px solid var(--brand); outline-offset: 2px; }

/* ---------- Official reference block ---------- */
.official-block {
  background: var(--surface); border: 1px solid var(--line);
  border-radius: var(--radius); box-shadow: var(--shadow);
  padding: 22px; margin: 26px 0;
}
.official-block .ob-head {
  display: flex; align-items: center; gap: 12px; flex-wrap: wrap; margin-bottom: 4px;
}
.official-block h2 { margin: 0; font-size: 21px; letter-spacing: -0.015em; }
.ob-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(min(200px, 100%), 1fr)); gap: 10px; margin-top: 16px; }
.ob-item {
  background: var(--given-bg); border: 1px solid #cbeedd; border-radius: 10px;
  padding: 10px 12px; text-align: center;
}
.ob-item .n { font-size: 12px; font-weight: 800; color: var(--given); text-transform: uppercase; letter-spacing: 0.04em; }
.ob-item .x { font-size: 16.5px; margin-top: 4px; overflow-x: auto; }
.ob-facts { margin: 14px 0 0; padding: 0; list-style: none; display: grid; gap: 6px; }
.ob-facts li { font-size: 13.5px; color: var(--ink-soft); display: flex; gap: 8px; align-items: baseline; }
.ob-facts li::before { content: "•"; color: var(--given); font-weight: 900; }
.tri-strip { display: flex; gap: 18px; flex-wrap: wrap; margin-top: 14px; justify-content: center; }
.tri-card { background: #fff; border: 1px solid var(--line); border-radius: 10px; padding: 12px 16px; text-align: center; }
.tri-card svg { display: block; margin: 0 auto 6px; }
.tri-card .n { font-size: 12px; font-weight: 800; color: var(--given); text-transform: uppercase; }

/* ---------- Desmos dual-pane ---------- */
.dual { display: grid; grid-template-columns: minmax(320px, 5fr) minmax(360px, 6fr); gap: 20px; align-items: start; }
.tech-list { display: flex; flex-direction: column; gap: 12px; animation: rise 0.5s cubic-bezier(0.2, 0.7, 0.3, 1) both; }
.tech-card {
  background: var(--surface); border: 1.5px solid var(--line); border-radius: var(--radius);
  padding: 16px 18px; cursor: pointer; scroll-margin-top: 90px;
  transition: border-color 0.12s ease, box-shadow 0.12s ease;
}
.tech-card:hover { border-color: var(--brand); }
.tech-card.on { border-color: var(--brand); box-shadow: 0 0 0 3px var(--brand-soft), var(--shadow); }
.tech-card .tc-top { display: flex; align-items: baseline; gap: 10px; }
.tech-card .num {
  font-size: 12px; font-weight: 900; color: var(--brand);
  background: var(--brand-soft); border-radius: 7px; padding: 2px 8px; flex: none;
}
.tech-card h3 { margin: 0; font-size: 16px; letter-spacing: -0.01em; flex: 1; }
.tech-card .signal { font-size: 13.5px; color: var(--ink-soft); margin: 8px 0 0; }
.tech-card .showcase { display: none; margin-top: 12px; flex-direction: column; gap: 10px; }
.tech-card.on .showcase { display: flex; }
.syntax-box {
  background: #14162b; color: #e8ebff; border-radius: 10px; padding: 12px 14px;
  font-family: var(--mono); font-size: 13.5px; white-space: pre-wrap; line-height: 1.6;
  display: flex; justify-content: space-between; gap: 14px; align-items: flex-start;
}
.copy-btn {
  flex: none; background: #2b2e57; color: #cdd3ff; border: none; cursor: pointer;
  font-size: 11.5px; font-weight: 800; border-radius: 7px; padding: 5px 10px;
  text-transform: uppercase; letter-spacing: 0.05em;
}
.copy-btn:hover { background: var(--brand); color: #fff; }
.tech-card .notes { font-size: 13px; color: var(--ink-soft); margin: 0; }
.calc-panel {
  position: sticky; top: 84px;
  background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius);
  box-shadow: var(--shadow); overflow: hidden;
}
.calc-panel .cp-head {
  display: flex; align-items: center; gap: 10px; padding: 12px 16px; border-bottom: 1px solid var(--line);
}
.calc-panel .cp-head .t { font-weight: 800; font-size: 14.5px; flex: 1; }
#calculator { height: 520px; }
.calc-loading { height: 520px; display: flex; align-items: center; justify-content: center; color: var(--ink-faint); font-size: 14px; }
.calc-fallback {
  height: 520px; display: flex; flex-direction: column; align-items: center; justify-content: center;
  gap: 16px; padding: 24px; text-align: center;
}
.calc-fallback .cf-label { font-size: 13px; font-weight: 800; text-transform: uppercase; letter-spacing: 0.06em; color: var(--ink-faint); }
.calc-fallback .cf-syntax { max-width: 420px; font-size: 16px; text-align: left; }
.calc-fallback .cf-note { font-size: 12.5px; color: var(--ink-faint); max-width: 420px; margin: 0; }

/* ---------- Diagnostic quiz ---------- */
.quiz-shell { max-width: 760px; margin: 0 auto; }
.quiz-top { display: flex; align-items: center; gap: 14px; margin-bottom: 14px; }
.quiz-top .score { font-size: 13.5px; font-weight: 800; color: var(--ink-soft); white-space: nowrap; }
.progress { flex: 1; height: 8px; border-radius: 999px; background: var(--line); overflow: hidden; }
.progress i { display: block; height: 100%; background: var(--brand); border-radius: 999px; transition: width 0.25s ease; }
.q-card {
  background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius);
  box-shadow: var(--shadow); padding: 26px;
  animation: rise 0.4s cubic-bezier(0.2, 0.7, 0.3, 1) both;
}
.q-card .q-domain { font-size: 12px; font-weight: 800; text-transform: uppercase; letter-spacing: 0.06em; color: var(--brand); margin-bottom: 10px; }
.q-card h2 { font-size: 20px; margin: 0 0 18px; letter-spacing: -0.01em; line-height: 1.35; }
.opts { display: grid; gap: 10px; }
.opt {
  text-align: left; width: 100%; cursor: pointer;
  background: #fff; border: 1.5px solid var(--line); border-radius: 12px;
  padding: 13px 16px; font-size: 15.5px; font-family: var(--font); color: var(--ink);
  display: flex; gap: 12px; align-items: center; transition: border-color 0.1s ease;
}
.opt:hover:not(:disabled) { border-color: var(--brand); }
.opt:active:not(:disabled) { transform: scale(0.99); }
.opt .k {
  flex: none; width: 26px; height: 26px; border-radius: 8px;
  display: inline-flex; align-items: center; justify-content: center;
  font-size: 12.5px; font-weight: 900; background: #f0f1f8; color: var(--ink-soft);
}
.opt > span:last-child { flex: 1; min-width: 0; }
.opt.right { border-color: var(--ok); background: #eefaf3; }
.opt.right .k { background: var(--ok); color: #fff; }
.opt.wrong { border-color: var(--bad); background: #fdeeee; }
.opt.wrong .k { background: var(--bad); color: #fff; }
.opt:disabled { cursor: default; opacity: 0.92; }
.explain {
  margin-top: 16px; border-left: 4px solid var(--brand); background: var(--brand-soft);
  border-radius: 0 10px 10px 0; padding: 12px 16px; font-size: 14.5px; color: var(--ink);
}
.q-foot { display: flex; justify-content: flex-end; margin-top: 18px; }
/* results */
.result-hero { text-align: center; padding: 10px 0 4px; }
.result-hero .big { font-size: 44px; font-weight: 900; letter-spacing: -0.03em; color: var(--brand); }
.result-hero .sub { color: var(--ink-soft); font-size: 15px; }
.gap-list { display: grid; gap: 10px; margin-top: 18px; }
.gap-item {
  display: flex; align-items: center; gap: 12px; flex-wrap: wrap;
  background: #fff; border: 1px solid var(--line); border-radius: 12px; padding: 13px 16px;
}
.gap-item .g-name { font-weight: 800; font-size: 15px; flex: 1; }
.gap-item .g-dom { font-size: 12px; color: var(--ink-faint); font-weight: 700; text-transform: uppercase; letter-spacing: 0.05em; }
.gap-item .g-links { display: flex; gap: 10px; font-size: 13.5px; font-weight: 800; }
.result-actions { display: flex; gap: 12px; justify-content: center; flex-wrap: wrap; margin-top: 26px; }
.all-good { text-align: center; color: var(--ok); font-weight: 800; padding: 16px 0 4px; }

/* ---------- Home feature cards ---------- */
.entry-grid { display: grid; grid-template-columns: 1.3fr 1fr 1fr; gap: 16px; margin: 10px 0 40px; }
.entry-card {
  background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius);
  box-shadow: var(--shadow); padding: 24px; display: flex; flex-direction: column; gap: 8px;
  transition: transform 0.18s ease, border-color 0.18s ease, box-shadow 0.18s ease;
  animation: rise 0.5s cubic-bezier(0.2, 0.7, 0.3, 1) both;
}
.entry-grid .entry-card:nth-child(2) { animation-delay: 0.07s; }
.entry-grid .entry-card:nth-child(3) { animation-delay: 0.14s; }
.entry-card:hover { transform: translateY(-2px); border-color: var(--brand); text-decoration: none; }
.entry-card .emoji { font-size: 26px; }
.entry-card h3 { margin: 0; font-size: 18px; letter-spacing: -0.01em; color: var(--ink); }
.entry-card p { margin: 0; color: var(--ink-soft); font-size: 14px; flex: 1; }
.entry-card .go { font-weight: 800; font-size: 14px; color: var(--brand); }
/* featured variant: primary action gets visual weight, not just another equal card */
.entry-card.featured {
  background: linear-gradient(160deg, #2623c9, #4441ef);
  border: none; color: #fff; position: relative; overflow: hidden;
}
.entry-card.featured::after {
  content: ""; position: absolute; inset: 0; pointer-events: none;
  background-image: radial-gradient(rgba(255, 255, 255, 0.14) 1px, transparent 1px);
  background-size: 18px 18px;
}
.entry-card.featured:hover { border-color: transparent; box-shadow: 0 12px 32px rgba(38, 35, 201, 0.35); }
.entry-card.featured h3 { color: #fff; }
.entry-card.featured p { color: rgba(255, 255, 255, 0.82); }
.entry-card.featured .go { color: #ffd76a; }
.entry-card.featured .start-tag {
  align-self: flex-start; font-size: 11px; font-weight: 900; letter-spacing: 0.1em;
  text-transform: uppercase; color: #2623c9; background: #ffd76a;
  border-radius: 999px; padding: 3px 10px;
}
/* editorial Q&A list (not another card grid) */
.qa-list { display: flex; flex-direction: column; }
.qa-item {
  padding: 18px 4px 18px 20px; border-left: 3px solid var(--line);
  transition: border-color 0.15s ease; animation: rise 0.5s cubic-bezier(0.2, 0.7, 0.3, 1) both;
}
.qa-list .qa-item:nth-child(2) { animation-delay: 0.07s; }
.qa-list .qa-item:nth-child(3) { animation-delay: 0.14s; }
.qa-item:hover { border-left-color: var(--brand); }
.qa-item h3 { margin: 0 0 6px; font-size: 17px; letter-spacing: -0.01em; }
.qa-item p { margin: 0; color: var(--ink-soft); font-size: 15px; max-width: 780px; }
.strip {
  background: var(--brand-deep); color: #fff; border-radius: var(--radius);
  padding: 22px 26px; display: flex; gap: 20px; align-items: center; flex-wrap: wrap;
  margin: 26px 0 10px;
}
.strip .s-num { font-size: 34px; font-weight: 900; letter-spacing: -0.02em; }
.strip .s-txt { flex: 1; min-width: 220px; font-size: 14.5px; color: #d9dcff; }
.strip a { color: #fff; font-weight: 800; border-bottom: 2px solid var(--brand); }

/* ---------- Footer ---------- */
.site-foot { border-top: 1px solid var(--line); margin-top: 70px; padding: 28px 0 40px; color: var(--ink-faint); font-size: 13px; }
.site-foot .f-row { display: flex; gap: 18px; flex-wrap: wrap; align-items: baseline; justify-content: space-between; }

/* ---------- Print ---------- */
.print-bar {
  display: flex; gap: 14px; align-items: center; flex-wrap: wrap;
  background: var(--brand-soft); border: 1px solid #d9d8ff; border-radius: var(--radius);
  padding: 14px 18px; margin: 18px 0; font-size: 14.5px;
}
@media print {
  .no-print { display: none !important; }
  body { background: #fff; }
  .site-head, .site-foot { display: none; }
  .card-grid { grid-template-columns: 1fr 1fr; gap: 8px; }
  .formula-card { box-shadow: none; border-color: #ccc; break-inside: avoid; }
  .official-block { box-shadow: none; }
  .section { break-inside: avoid-page; }
  a { color: var(--ink); text-decoration: none; }
  .formula-card details { display: block; }
  .formula-card details summary { display: none; }
}

/* ---------- Responsive ---------- */
@media (max-width: 900px) {
  .dual { grid-template-columns: 1fr; }
  .calc-panel { position: static; }
  #calculator { height: 420px; }
  /* entry cards: featured spans the first row, two cards below */
  .entry-grid { grid-template-columns: 1fr 1fr; }
  .entry-card.featured { grid-column: 1 / -1; }
}
@media (max-width: 640px) {
  .site-head .row { height: 54px; gap: 8px; }
  .logo { font-size: 16px; }
  .nav-links { gap: 2px; }
  .nav-links a { padding: 7px 10px; font-size: 14px; }
  .nav-full { display: none; }
  .nav-short { display: inline; }
  .hero { padding: 36px 0 28px; }
  .hero h1 { font-size: clamp(27px, 8vw, 34px); }
  .hero p.lede { font-size: 16px; }
  .hero-actions .btn { padding: 12px 18px; font-size: 15px; }
  .strip { padding: 18px 20px; }
  .strip .s-num { font-size: 28px; }
  .entry-grid { grid-template-columns: 1fr; }
  .entry-card.featured { grid-column: auto; }
  .qa-item { padding: 14px 2px 14px 14px; }
  .qa-item p { font-size: 14.5px; }
  /* avoid iOS focus-zoom: inputs must be >= 16px */
  #formula-search { font-size: 16px; }
  .chip { padding: 9px 14px; }
  #calculator { height: 360px; }
  .calc-fallback { height: 360px; }
  .q-card { padding: 20px 16px; }
  .formula-card { padding: 16px 14px 12px; }
  .section > h2 { font-size: 19px; }
  .official-block { padding: 16px; }
  .site-foot .f-row { justify-content: flex-start; }
}
/* touch devices: roomier tap targets, no hover-only affordance */
@media (hover: none) {
  .chip { padding: 10px 16px; }
  .copy-btn { padding: 7px 12px; }
  .formula-card:hover { transform: none; }
  .entry-card:hover { transform: none; }
}