:root {
  --df-blue: #0b1e3d;
  --df-blue-deep: #07152d;
  --df-white: #f7fbff;
  --df-muted: rgba(247, 251, 255, 0.74);
  --df-line: rgba(247, 251, 255, 0.18);
  --df-line-strong: rgba(247, 251, 255, 0.32);
  --df-card: rgba(5, 16, 36, 0.74);
  --df-card-soft: rgba(11, 30, 61, 0.66);
  --df-cyan: #c2dcff;
  --df-cyan-strong: #e1efff;
  --df-shadow: 0 24px 85px rgba(0, 0, 0, 0.42);
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  min-height: 100vh;
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  color: var(--df-white);
  background: var(--df-blue);
}

a { color: var(--df-cyan-strong); }

.background-video {
  position: fixed;
  inset: 0;
  width: 100%;
  height: 100%;
  object-fit: cover;
  opacity: 0.78;
  filter: contrast(1.34) saturate(1.12) brightness(0.98);
  z-index: -3;
}

.background-overlay {
  position: fixed;
  inset: 0;
  background:
    radial-gradient(circle at 18% 16%, rgba(220, 238, 255, 0.18), transparent 34rem),
    radial-gradient(circle at 82% 76%, rgba(185, 215, 255, 0.14), transparent 36rem),
    linear-gradient(180deg, rgba(11, 30, 61, 0.38), rgba(11, 30, 61, 0.78) 52%, #0b1e3d 100%);
  z-index: -2;
}

.top-banner {
  position: sticky;
  top: 0;
  z-index: 50;
  background: #0b1e3d;
  border-bottom: 1px solid var(--df-line);
  box-shadow: 0 12px 34px rgba(0, 0, 0, 0.28);
}

.banner-inner {
  width: min(1240px, calc(100% - 2rem));
  margin: 0 auto;
  min-height: 106px;
  display: flex;
  justify-content: center;
  align-items: center;
  padding: 0.55rem 0;
}

.banner-logo {
  display: block;
  width: min(980px, 92vw);
  height: auto;
  max-height: 128px;
  object-fit: contain;
}

.page-shell {
  width: min(1180px, calc(100% - 2rem));
  margin: 0 auto;
  padding: clamp(2.2rem, 6vw, 5.5rem) 0 5rem;
}

.hero-grid {
  display: grid;
  grid-template-columns: minmax(0, 1.18fr) minmax(330px, 0.82fr);
  gap: clamp(1.25rem, 4vw, 3rem);
  align-items: center;
}

.kicker {
  font-size: 0.78rem;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--df-cyan);
  font-weight: 850;
}

h1, h2, h3 { margin: 0; line-height: 1.05; }
h1 {
  margin-top: 0.8rem;
  font-size: clamp(3.2rem, 8.5vw, 7.4rem);
  letter-spacing: -0.065em;
}

h2 { font-size: clamp(1.7rem, 3.8vw, 3.2rem); }
h3 { font-size: 1.1rem; }

.lede {
  max-width: 780px;
  margin: 1.1rem 0 0;
  font-size: clamp(1.08rem, 2vw, 1.42rem);
  line-height: 1.62;
  color: var(--df-muted);
}

.hero-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.85rem;
  margin-top: 1.75rem;
}

.button,
button {
  appearance: none;
  border: 1px solid rgba(255,255,255,0.28);
  border-radius: 999px;
  background: #f7fbff;
  color: #0b1e3d;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  min-height: 46px;
  padding: 0.78rem 1.14rem;
  font-weight: 850;
  text-decoration: none;
  cursor: pointer;
}

.button.secondary,
button.secondary {
  background: rgba(255,255,255,0.08);
  color: var(--df-white);
}

.card {
  background: var(--df-card);
  border: 1px solid var(--df-line);
  border-radius: 24px;
  box-shadow: var(--df-shadow);
  backdrop-filter: blur(18px);
}

.login-card { padding: clamp(1.25rem, 3vw, 1.9rem); }
.login-card h2 { margin-top: 0.45rem; font-size: 1.6rem; }
.login-card p, .login-note { color: var(--df-muted); line-height: 1.55; }

.form-row { margin-top: 1rem; }
label {
  display: block;
  margin-bottom: 0.42rem;
  color: rgba(255,255,255,0.84);
  font-size: 0.84rem;
  font-weight: 780;
}
input {
  display: block;
  width: 100%;
  min-height: 48px;
  border: 1px solid rgba(255,255,255,0.24);
  border-radius: 14px;
  padding: 0.72rem 0.86rem;
  background: rgba(0,0,0,0.24);
  color: var(--df-white);
  outline: none;
}
input:focus { border-color: rgba(194, 220, 255, 0.82); }
.login-card button { width: 100%; margin-top: 1.15rem; }
.login-note, .status-note { margin-top: 0.85rem; font-size: 0.88rem; }
.status-note.error { color: #fecaca; }
.status-note.ok { color: #bbf7d0; }

.section { margin-top: clamp(2rem, 6vw, 5rem); }
.section-copy {
  max-width: 900px;
  color: var(--df-muted);
  line-height: 1.66;
  font-size: 1.06rem;
}

.feature-grid,
.equation-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 1rem;
  margin-top: 1.25rem;
}
.feature-card,
.equation-card {
  padding: 1.1rem;
  background: rgba(255,255,255,0.07);
  border: 1px solid var(--df-line);
  border-radius: 18px;
}
.feature-card p,
.equation-card p,
.tech-content p,
.tech-content li { color: var(--df-muted); line-height: 1.62; }
.feature-card h3,
.equation-card h3 { margin-bottom: 0.55rem; }

.tech-layout {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 290px;
  gap: 1.25rem;
  align-items: start;
}
.tech-content { padding: clamp(1.05rem, 3vw, 2rem); }
.tech-content h2 { margin-top: 2.15rem; font-size: 1.7rem; }
.tech-content h2:first-child { margin-top: 0; }
.tech-content h3 { margin-top: 1.4rem; font-size: 1.08rem; }
.toc { padding: 1rem; position: sticky; top: 126px; }
.toc a { display: block; padding: 0.45rem 0; text-decoration: none; color: var(--df-muted); }
.toc a:hover { color: var(--df-white); }

.equation {
  margin: 1rem 0;
  padding: 1rem;
  overflow-x: auto;
  border: 1px solid var(--df-line);
  border-radius: 16px;
  background: rgba(255,255,255,0.08);
  font-family: "Times New Roman", ui-serif, Georgia, serif;
  font-size: 1.14rem;
}
.callout {
  margin: 1.2rem 0;
  padding: 1rem;
  border-left: 4px solid var(--df-cyan);
  background: rgba(194, 220, 255, 0.09);
  border-radius: 16px;
}
.footer {
  width: min(1180px, calc(100% - 2rem));
  margin: 0 auto;
  padding: 2rem 0 3rem;
  color: rgba(255,255,255,0.56);
  border-top: 1px solid var(--df-line);
}
code { color: var(--df-cyan); }

@media (max-width: 900px) {
  .hero-grid, .tech-layout { grid-template-columns: 1fr; }
  .feature-grid, .equation-grid { grid-template-columns: 1fr; }
  .toc { position: static; }
  .banner-inner { min-height: 84px; }
  .banner-logo { width: 92vw; }
}