:root {
  --bg-deep: #05060f;
  --bg-navy: #0a0e1a;
  --glass: rgba(255, 255, 255, 0.05);
  --glass-strong: rgba(255, 255, 255, 0.08);
  --glass-border: rgba(255, 255, 255, 0.12);
  --glass-border-hover: rgba(255, 255, 255, 0.22);
  --blue: #f59e0b;
  --blue-bright: #fbbf24;
  --blue-glow: rgba(251, 191, 36, 0.45);
  --blue-glow-soft: rgba(251, 191, 36, 0.18);
  --cyan: #fb923c;
  --text: #f4f7ff;
  --text-muted: #8b95b0;
  --text-dim: #5a6478;
  --correct: #4ade80;
  --incorrect: #f87171;
  --warn: #fbbf24;
  --radius: 20px;
  --radius-pill: 999px;
}
* { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body {
  font-family: "Inter", system-ui, -apple-system, sans-serif;
  background: var(--bg-deep);
  color: var(--text);
  min-height: 100vh;
  line-height: 1.6;
  overflow-x: hidden;
  position: relative;
}
body::before, body::after {
  content: "";
  position: fixed;
  border-radius: 50%;
  filter: blur(100px);
  pointer-events: none;
  z-index: 0;
}
body::before {
  width: 520px; height: 520px;
  top: -120px; left: 50%;
  transform: translateX(-60%);
  background: radial-gradient(circle, rgba(251, 191, 36, 0.35) 0%, transparent 70%);
  animation: floatGlow 12s ease-in-out infinite alternate;
}
body::after {
  width: 420px; height: 420px;
  bottom: 10%; right: -80px;
  background: radial-gradient(circle, rgba(249, 115, 22, 0.2) 0%, transparent 70%);
  animation: floatGlow 14s ease-in-out infinite alternate-reverse;
}
@keyframes floatGlow {
  from { transform: translateX(-60%) translateY(0); }
  to { transform: translateX(-50%) translateY(24px); }
}
.glow-left {
  position: fixed;
  width: 380px; height: 380px;
  bottom: 20%; left: -100px;
  background: radial-gradient(circle, rgba(251, 191, 36, 0.15) 0%, transparent 70%);
  filter: blur(80px);
  pointer-events: none;
  z-index: 0;
}
.wrap {
  position: relative;
  z-index: 1;
  max-width: 960px;
  margin: 0 auto;
  padding: 24px 20px 48px;
}
.wrap.wide { max-width: 1100px; }
header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  margin-bottom: 28px;
  flex-wrap: wrap;
}
.logo {
  display: flex;
  align-items: center;
  gap: 12px;
  text-decoration: none;
  color: var(--text);
}
.logo-mark {
  width: 40px; height: 40px;
  border-radius: 12px;
  background: linear-gradient(135deg, rgba(251, 191, 36, 0.35), rgba(249, 115, 22, 0.15));
  border: 1px solid var(--glass-border);
  display: grid;
  place-items: center;
  box-shadow: 0 0 24px var(--blue-glow-soft);
}
.logo-mark svg {
  width: 20px; height: 20px;
  stroke: var(--blue-bright);
  fill: none;
  stroke-width: 2;
  stroke-linecap: round;
  stroke-linejoin: round;
}
.logo-text { font-weight: 700; font-size: 1.15rem; letter-spacing: -0.02em; }
.logo-text span { color: var(--blue-bright); }
.nav-pills { display: flex; gap: 8px; flex-wrap: wrap; }
.pill {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 8px 16px;
  border-radius: var(--radius-pill);
  background: var(--glass);
  border: 1px solid var(--glass-border);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  color: var(--text-muted);
  font-size: 0.85rem;
  font-weight: 500;
  text-decoration: none;
  transition: border-color 0.2s, color 0.2s, background 0.2s;
}
.pill:hover, .pill.active {
  border-color: var(--glass-border-hover);
  color: var(--text);
  background: var(--glass-strong);
}
.pill.active { border-color: rgba(251, 191, 36, 0.45); color: var(--blue-bright); }
.ad-slot {
  border: 1.5px dashed rgba(251, 191, 36, 0.35);
  border-radius: 14px;
  background: rgba(251, 191, 36, 0.04);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 4px;
  color: var(--text-dim);
  font-size: 0.75rem;
  font-weight: 500;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  margin-bottom: 24px;
}
.ad-slot::before { content: "Ad space"; font-size: 0.7rem; opacity: 0.7; }
.ad-slot.banner {
  width: 100%; max-width: 728px; height: 90px;
  margin-left: auto; margin-right: auto;
}
.ad-slot .size-label {
  font-size: 0.65rem; color: var(--text-dim); opacity: 0.8;
  text-transform: none; letter-spacing: 0;
}
.glass {
  background: var(--glass);
  border: 1px solid var(--glass-border);
  border-radius: var(--radius);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
}
.hero { text-align: center; margin-bottom: 28px; }
.hero h1 {
  font-size: clamp(1.6rem, 4vw, 2.2rem);
  font-weight: 700;
  letter-spacing: -0.03em;
  margin-bottom: 10px;
}
.hero p { color: var(--text-muted); max-width: 640px; margin: 0 auto; font-size: 1.02rem; }
.article {
  padding: 32px 28px;
  margin-bottom: 24px;
}
.article h2 {
  font-size: 1.25rem;
  font-weight: 700;
  letter-spacing: -0.02em;
  margin: 28px 0 12px;
  color: var(--text);
}
.article h2:first-child { margin-top: 0; }
.article h3 {
  font-size: 1.05rem;
  font-weight: 600;
  margin: 20px 0 8px;
  color: var(--blue-bright);
}
.article p { color: var(--text-muted); margin-bottom: 14px; }
.article ul, .article ol {
  color: var(--text-muted);
  margin: 0 0 16px 1.25rem;
}
.article li { margin-bottom: 8px; }
.article a { color: var(--blue-bright); text-decoration: none; }
.article a:hover { text-decoration: underline; }
.article strong { color: var(--text); font-weight: 600; }
.cta-box {
  margin-top: 28px;
  padding: 20px 22px;
  border-radius: 16px;
  background: rgba(251, 191, 36, 0.1);
  border: 1px solid rgba(251, 191, 36, 0.3);
  text-align: center;
}
.cta-box p { color: var(--text-muted); margin-bottom: 14px; }
.btn {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 12px 22px;
  border-radius: var(--radius-pill);
  font-weight: 600;
  font-size: 0.95rem;
  text-decoration: none;
  border: none;
  cursor: pointer;
  font-family: inherit;
  transition: transform 0.15s, box-shadow 0.15s, background 0.15s;
}
.btn-primary {
  background: linear-gradient(135deg, var(--blue), #d97706);
  color: #fff;
  box-shadow: 0 4px 24px var(--blue-glow-soft);
}
.btn-primary:hover { transform: translateY(-1px); box-shadow: 0 6px 28px var(--blue-glow); }
.btn-ghost {
  background: var(--glass);
  border: 1px solid var(--glass-border);
  color: var(--text-muted);
}
.btn-ghost:hover {
  border-color: var(--glass-border-hover);
  color: var(--text);
  background: var(--glass-strong);
}
.btn-danger {
  background: rgba(248, 113, 113, 0.12);
  border: 1px solid rgba(248, 113, 113, 0.35);
  color: #fca5a5;
}
.btn-danger:hover { background: rgba(248, 113, 113, 0.2); }
.grade-table { width: 100%; border-collapse: collapse; margin: 12px 0 22px; font-size: 0.92rem; }
.grade-table th, .grade-table td {
  text-align: left; padding: 12px 14px;
  border-bottom: 1px solid var(--glass-border);
}
.grade-table th { color: var(--blue-bright); font-weight: 600; }
.grade-table td { color: var(--text-muted); }
.grade-table tr:hover td { background: rgba(255,255,255,0.03); }
.related {
  display: grid;
  gap: 12px;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  margin-top: 8px;
}
.related a {
  display: block;
  padding: 16px 18px;
  border-radius: 14px;
  background: var(--glass);
  border: 1px solid var(--glass-border);
  color: var(--text);
  text-decoration: none;
  transition: border-color 0.2s, background 0.2s;
}
.related a:hover {
  border-color: var(--glass-border-hover);
  background: var(--glass-strong);
}
.related a span { display: block; color: var(--text-muted); font-size: 0.85rem; margin-top: 4px; font-weight: 400; }
footer {
  margin-top: 40px;
  padding-top: 24px;
  border-top: 1px solid var(--glass-border);
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  color: var(--text-dim);
  font-size: 0.8rem;
}
footer a { color: var(--text-muted); text-decoration: none; transition: color 0.2s; }
footer a:hover { color: var(--blue-bright); }
.footer-links { display: flex; gap: 16px; flex-wrap: wrap; }
@media (max-width: 600px) {
  .article { padding: 22px 18px; }
  .ad-slot.banner { height: 60px; }
}
/* --- SEO guide pages --- */
.faq-list details{background:var(--glass);border:1px solid var(--glass-border);border-radius:14px;padding:14px 18px;margin-bottom:10px;transition:border-color .2s}
.faq-list details[open]{border-color:var(--glass-border-hover)}
.faq-list summary{cursor:pointer;font-weight:600;list-style:none;color:var(--text)}
.faq-list summary::-webkit-details-marker{display:none}
.faq-list summary::after{content:"+";float:right;color:var(--blue-bright);font-weight:700}
.faq-list details[open] summary::after{content:"−"}
.faq-list details p{color:var(--text-muted);margin-top:10px;margin-bottom:0}
.table-wrap{overflow-x:auto;-webkit-overflow-scrolling:touch}
.article code{background:var(--glass-strong);border:1px solid var(--glass-border);border-radius:6px;padding:1px 6px;font-size:.88em;color:var(--cyan)}
.formula{background:var(--blue-glow-soft);border:1px solid var(--glass-border);border-left:3px solid var(--blue-bright);border-radius:12px;padding:14px 18px;margin:12px 0 18px;color:var(--text);font-weight:600}
.article ol li::marker,.article ul li::marker{color:var(--blue-bright)}