/* Periodic Table - Chem landing site
   Palette derived from app icon: royal blue #1552B4, white, coral #F2695C */

:root {
  --blue: #1552b4;
  --blue-dark: #0e3c87;
  --blue-deep: #0a2d66;
  --coral: #f2695c;
  --coral-dark: #c94437;
  --ink: #17233b;
  --ink-soft: #46536d;
  --bg: #f7f9fd;
  --surface: #ffffff;
  --line: #dce4f2;
  --tile: #eaf0fb;
  --focus: #f2695c;
  --radius: 12px;
  --shadow: 0 8px 28px rgba(14, 60, 135, 0.12);
}

@media (prefers-color-scheme: dark) {
  :root {
    --blue: #5b8de0;
    --blue-dark: #7da8ec;
    --blue-deep: #0a2d66;
    --coral: #f58174;
    --coral-dark: #f2695c;
    --ink: #e8edf7;
    --ink-soft: #a9b6cf;
    --bg: #0d1424;
    --surface: #16203a;
    --line: #2a3757;
    --tile: #1c2946;
    --shadow: 0 8px 28px rgba(0, 0, 0, 0.45);
  }
}

* { box-sizing: border-box; }

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

body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  color: var(--ink);
  background: var(--bg);
  line-height: 1.65;
  font-size: 1.0625rem;
}

img { max-width: 100%; height: auto; }

a { color: var(--blue); }
a:hover { color: var(--coral-dark); }

:focus-visible {
  outline: 3px solid var(--focus);
  outline-offset: 2px;
  border-radius: 4px;
}

.skip-link {
  position: absolute;
  left: -999px;
  top: 0;
  background: var(--blue-deep);
  color: #fff;
  padding: 0.6rem 1rem;
  z-index: 100;
  border-radius: 0 0 8px 0;
}
.skip-link:focus { left: 0; }

.wrap {
  max-width: 1080px;
  margin: 0 auto;
  padding: 0 1.25rem;
}

/* ---------- Header / nav ---------- */
.site-header {
  background: var(--surface);
  border-bottom: 1px solid var(--line);
  position: sticky;
  top: 0;
  z-index: 50;
}
.nav-bar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: 0.7rem 0;
}
.brand {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  font-weight: 700;
  font-size: 1.1rem;
  color: var(--ink);
  text-decoration: none;
}
.brand img { border-radius: 22%; }
.nav-links {
  display: flex;
  gap: 1.25rem;
  list-style: none;
  margin: 0;
  padding: 0;
  align-items: center;
}
.nav-links a {
  text-decoration: none;
  color: var(--ink-soft);
  font-weight: 500;
}
.nav-links a:hover { color: var(--blue); }
.nav-links .nav-cta {
  background: var(--blue);
  color: #fff;
  padding: 0.45rem 0.95rem;
  border-radius: 8px;
}
.nav-links .nav-cta:hover { background: var(--blue-dark); color: #fff; }
@media (prefers-color-scheme: dark) {
  .nav-links .nav-cta { background: #1552b4; }
  .nav-links .nav-cta:hover { background: #2a69cf; }
}

.nav-toggle {
  display: none;
  background: none;
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 0.45rem 0.6rem;
  cursor: pointer;
  color: var(--ink);
  font-size: 1.2rem;
  line-height: 1;
}

@media (max-width: 720px) {
  .nav-toggle { display: block; }
  .nav-links {
    display: none;
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    flex-direction: column;
    align-items: stretch;
    background: var(--surface);
    border-bottom: 1px solid var(--line);
    padding: 0.75rem 1.25rem 1.25rem;
    gap: 0.9rem;
    box-shadow: var(--shadow);
  }
  .nav-links.open { display: flex; }
}

/* ---------- Hero ---------- */
.hero {
  background: linear-gradient(160deg, var(--blue-deep) 0%, #1552b4 55%, #2a69cf 100%);
  color: #fff;
  padding: 4rem 0 4.5rem;
  overflow: hidden;
}
.hero-grid {
  display: grid;
  grid-template-columns: 1.15fr 0.85fr;
  gap: 3rem;
  align-items: center;
}
@media (max-width: 820px) {
  .hero-grid { grid-template-columns: 1fr; }
}
.hero h1 {
  font-size: clamp(1.9rem, 4.5vw, 2.9rem);
  line-height: 1.15;
  margin: 0 0 1rem;
  letter-spacing: -0.02em;
}
.hero h1 .accent { color: #ffb3aa; }
.hero p.lede {
  font-size: 1.15rem;
  color: #d7e3f8;
  margin: 0 0 1.75rem;
  max-width: 34rem;
}
.hero-badges { display: flex; flex-wrap: wrap; gap: 0.9rem; align-items: center; }
.store-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.65rem;
  background: #000;
  color: #fff;
  text-decoration: none;
  padding: 0.6rem 1.2rem;
  border-radius: 10px;
  border: 1px solid rgba(255, 255, 255, 0.35);
  line-height: 1.2;
}
.store-badge:hover { background: #1a1a1a; color: #fff; }
.store-badge .apple-mark { width: 26px; height: 26px; flex: none; }
.store-badge small { display: block; font-size: 0.68rem; opacity: 0.85; }
.store-badge strong { font-size: 1.05rem; font-weight: 600; }
.hero-note { font-size: 0.9rem; color: #b9cdf0; margin-top: 1rem; }

/* Decorative element-tile mock */
.tile-mock {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 0.7rem;
  max-width: 330px;
  margin: 0 auto;
  transform: rotate(2deg);
}
.el-tile {
  background: rgba(255, 255, 255, 0.1);
  border: 1px solid rgba(255, 255, 255, 0.28);
  border-radius: 10px;
  padding: 0.55rem 0.65rem;
  text-align: left;
  backdrop-filter: blur(2px);
}
.el-tile .num { font-size: 0.7rem; color: #ffb3aa; display: block; }
.el-tile .sym { font-size: 1.6rem; font-weight: 700; display: block; line-height: 1.1; }
.el-tile .mass { font-size: 0.7rem; color: #c4d6f5; display: block; }
.el-tile.hot { background: rgba(242, 105, 92, 0.28); border-color: rgba(255, 179, 170, 0.6); }

/* ---------- Sections ---------- */
section { padding: 3.5rem 0; }
section h2 {
  font-size: clamp(1.5rem, 3vw, 2.1rem);
  letter-spacing: -0.01em;
  margin: 0 0 0.5rem;
}
.section-lede { color: var(--ink-soft); max-width: 44rem; margin: 0 0 2rem; }

.alt-bg { background: var(--surface); border-top: 1px solid var(--line); border-bottom: 1px solid var(--line); }

/* Problem / solution */
.split {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 2rem;
}
@media (max-width: 720px) { .split { grid-template-columns: 1fr; } }
.panel {
  background: var(--tile);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 1.6rem 1.6rem 1.2rem;
}
.panel.solution { border-top: 4px solid var(--coral); }
.panel.problem { border-top: 4px solid var(--blue); }
.panel h3 { margin-top: 0; }
.panel ul { padding-left: 1.2rem; margin: 0.5rem 0 0.75rem; }
.panel li { margin-bottom: 0.5rem; }

/* Feature cards */
.feature-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 1.25rem;
}
.feature {
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 1.4rem 1.4rem 1.1rem;
  box-shadow: 0 2px 8px rgba(14, 60, 135, 0.05);
}
.feature .chip {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 44px;
  height: 44px;
  border-radius: 10px;
  background: var(--blue);
  color: #fff;
  font-weight: 700;
  font-size: 1rem;
  margin-bottom: 0.8rem;
}
.feature:nth-child(even) .chip { background: var(--coral-dark); }
@media (prefers-color-scheme: dark) {
  .feature .chip { background: #1552b4; }
  .feature:nth-child(even) .chip { background: #c94437; }
}
.feature h3 { margin: 0 0 0.4rem; font-size: 1.1rem; }
.feature p { margin: 0; color: var(--ink-soft); font-size: 0.97rem; }
.feature .premium-tag {
  display: inline-block;
  font-size: 0.72rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--coral-dark);
  margin-top: 0.6rem;
}

/* How it helps */
.steps { list-style: none; margin: 0; padding: 0; counter-reset: step; display: grid; gap: 1.1rem; max-width: 46rem; }
.steps li {
  counter-increment: step;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 1.1rem 1.3rem 1.1rem 4rem;
  position: relative;
}
.steps li::before {
  content: counter(step);
  position: absolute;
  left: 1.1rem;
  top: 1.1rem;
  width: 2rem;
  height: 2rem;
  border-radius: 50%;
  background: var(--coral);
  color: #fff;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
}
.steps h3 { margin: 0 0 0.2rem; font-size: 1.05rem; }
.steps p { margin: 0; color: var(--ink-soft); font-size: 0.97rem; }

/* FAQ accordion */
.faq-list { max-width: 46rem; }
.faq-item { border: 1px solid var(--line); border-radius: 10px; margin-bottom: 0.8rem; background: var(--surface); }
.faq-q {
  width: 100%;
  text-align: left;
  background: none;
  border: 0;
  padding: 1rem 3rem 1rem 1.2rem;
  font: inherit;
  font-weight: 600;
  color: var(--ink);
  cursor: pointer;
  position: relative;
}
.faq-q::after {
  content: "+";
  position: absolute;
  right: 1.1rem;
  top: 50%;
  transform: translateY(-50%);
  font-size: 1.4rem;
  color: var(--coral-dark);
  transition: transform 0.2s;
}
.faq-q[aria-expanded="true"]::after { content: "\2212"; }
.faq-a { padding: 0 1.2rem 1.1rem; color: var(--ink-soft); }
.faq-a[hidden] { display: none; }
.faq-a p { margin: 0; }

/* Guides teaser */
.guide-cards { display: grid; grid-template-columns: repeat(auto-fit, minmax(230px, 1fr)); gap: 1.25rem; }
.guide-card {
  display: block;
  background: var(--surface);
  border: 1px solid var(--line);
  border-left: 4px solid var(--blue);
  border-radius: var(--radius);
  padding: 1.3rem 1.3rem 1.1rem;
  text-decoration: none;
  color: var(--ink);
  transition: transform 0.15s ease, box-shadow 0.15s ease;
}
.guide-card:hover { transform: translateY(-3px); box-shadow: var(--shadow); color: var(--ink); }
.guide-card h3 { margin: 0 0 0.4rem; font-size: 1.05rem; color: var(--blue); }
.guide-card p { margin: 0; font-size: 0.94rem; color: var(--ink-soft); }

/* CTA band */
.cta-band {
  background: linear-gradient(135deg, var(--blue-deep), #1552b4);
  color: #fff;
  text-align: center;
  border-radius: var(--radius);
  padding: 3rem 1.5rem;
}
.cta-band h2 { color: #fff; }
.cta-band p { color: #cfdef7; max-width: 36rem; margin: 0.5rem auto 1.6rem; }

/* ---------- Footer ---------- */
.site-footer {
  background: var(--blue-deep);
  color: #c4d6f5;
  padding: 2.75rem 0 2rem;
  margin-top: 3rem;
  font-size: 0.95rem;
}
.footer-grid { display: grid; grid-template-columns: 1.2fr 1fr 1fr; gap: 2rem; }
@media (max-width: 720px) { .footer-grid { grid-template-columns: 1fr; } }
.site-footer h3 { color: #fff; font-size: 1rem; margin: 0 0 0.6rem; }
.site-footer ul { list-style: none; margin: 0; padding: 0; }
.site-footer li { margin-bottom: 0.45rem; }
.site-footer a { color: #d7e3f8; }
.site-footer a:hover { color: #ffb3aa; }
.footer-bottom { border-top: 1px solid rgba(255, 255, 255, 0.18); margin-top: 2rem; padding-top: 1.25rem; font-size: 0.85rem; color: #9db4dd; }

/* ---------- Guide / article pages ---------- */
.article-header { background: var(--surface); border-bottom: 1px solid var(--line); padding: 2.5rem 0 2rem; }
.breadcrumb { font-size: 0.88rem; color: var(--ink-soft); margin-bottom: 0.9rem; }
.breadcrumb ol { list-style: none; display: flex; flex-wrap: wrap; gap: 0.4rem; margin: 0; padding: 0; }
.breadcrumb li + li::before { content: "/"; margin-right: 0.4rem; color: var(--line); }
.article-header h1 { font-size: clamp(1.7rem, 4vw, 2.4rem); line-height: 1.2; margin: 0 0 0.5rem; letter-spacing: -0.02em; }
.article-meta { color: var(--ink-soft); font-size: 0.92rem; }

.article-body { max-width: 46rem; margin: 0 auto; padding: 2.5rem 1.25rem 3rem; }
.article-body h2 { font-size: 1.5rem; margin: 2.2rem 0 0.7rem; letter-spacing: -0.01em; }
.article-body h3 { font-size: 1.15rem; margin: 1.6rem 0 0.5rem; }
.article-body table {
  border-collapse: collapse;
  width: 100%;
  margin: 1.2rem 0;
  font-size: 0.95rem;
}
.article-body th, .article-body td {
  border: 1px solid var(--line);
  padding: 0.55rem 0.75rem;
  text-align: left;
}
.article-body th { background: var(--tile); }
.article-body code {
  background: var(--tile);
  border: 1px solid var(--line);
  border-radius: 5px;
  padding: 0.1rem 0.35rem;
  font-size: 0.92em;
  font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
}
.callout {
  background: var(--tile);
  border-left: 4px solid var(--coral);
  border-radius: 0 10px 10px 0;
  padding: 1rem 1.25rem;
  margin: 1.5rem 0;
}
.callout p { margin: 0.3rem 0; }
.app-help {
  background: var(--surface);
  border: 1px solid var(--line);
  border-top: 4px solid var(--blue);
  border-radius: var(--radius);
  padding: 1.5rem 1.5rem 1.25rem;
  margin: 2.5rem 0 1rem;
  box-shadow: var(--shadow);
}
.app-help h2 { margin-top: 0; }
.related { margin-top: 2.5rem; padding-top: 1.5rem; border-top: 1px solid var(--line); }
.related h2 { font-size: 1.2rem; margin-top: 0; }
.related ul { padding-left: 1.2rem; }

.btn {
  display: inline-block;
  background: var(--coral-dark);
  color: #fff;
  text-decoration: none;
  font-weight: 600;
  padding: 0.65rem 1.3rem;
  border-radius: 9px;
}
.btn:hover { background: #a83428; color: #fff; }
@media (prefers-color-scheme: dark) {
  .btn { background: #f2695c; color: #1a0c0a; }
  .btn:hover { background: #f58174; color: #1a0c0a; }
}

@media (max-width: 400px) {
  body { font-size: 1rem; }
  .hero { padding: 3rem 0; }
  section { padding: 2.5rem 0; }
}