/* ==================================================
   NAVIGATION (MINIMAL, THIN, ADAPTIVE OVER HERO)
   ================================================== */
.site-header {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  z-index: 1000;
  padding: 1.5rem var(--container-padding);
  background: transparent;
  transition: background-color 0.4s ease, backdrop-filter 0.4s ease, border-color 0.4s ease, padding 0.4s ease;
}

.site-header.scrolled {
  background-color: var(--bg-elevated);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  border-bottom: 1px solid var(--border-subtle);
  padding: 1rem var(--container-padding);
  box-shadow: var(--shadow-sm);
}

.nav-container {
  max-width: var(--container-max-width);
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.brand-logo {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  font-family: var(--font-main);
  font-weight: 800;
  font-size: 1.2rem;
  letter-spacing: -0.03em;
  color: var(--text-primary);
  text-shadow: 0 1px 4px rgba(0, 0, 0, 0.2);
}

.brand-logo .math-symbol {
  color: var(--accent-blue);
  font-weight: 700;
  font-family: var(--font-mono);
  font-size: 1.35rem;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: 2.5rem;
  list-style: none;
}

.nav-link {
  font-size: 0.9375rem;
  font-weight: 500;
  color: var(--text-secondary);
  position: relative;
  padding: 0.25rem 0;
  letter-spacing: -0.01em;
}

.nav-link::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 0;
  width: 0;
  height: 2px;
  background-color: var(--accent-blue);
  transition: width 0.3s var(--transition-smooth);
}

.nav-link:hover {
  color: var(--text-primary);
}

.nav-link:hover::after {
  width: 100%;
}

.nav-right {
  display: flex;
  align-items: center;
  gap: 1.25rem;
}

.nav-tagline {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  letter-spacing: 0.15em;
  text-transform: uppercase;
  color: var(--text-muted);
}

.nav-menu-btn {
  display: none;
  background: none;
  border: 1px solid var(--border-subtle);
  border-radius: 50%;
  width: 40px;
  height: 40px;
  cursor: pointer;
  align-items: center;
  justify-content: center;
  color: var(--text-primary);
  transition: all 0.25s ease;
}

.nav-menu-btn:hover {
  background-color: var(--bg-surface-subtle);
  border-color: var(--border-strong);
}

/* ==================================================
   01 — HERO (VIDEO + ONE MINIMAL WELCOME HEADLINE)
   - Hero video remains the dominant visual
   - Only ONE quiet welcoming text: "Welcome to MatheReality."
   - 100vh height with 16:9 responsive frame
   - Cursor-based floating inertia on video only
   - Stable centered welcome headline
   ================================================== */
.hero-section {
  position: relative;
  width: 100%;
  height: 100vh;
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  overflow: hidden;
  background-color: #000000;
  perspective: 1000px;
  z-index: 10;
}

.hero-video-viewport {
  position: relative;
  width: 100%;
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  transform-style: preserve-3d;
  will-change: transform;
}

.hero-video-frame {
  position: relative;
  width: 100%;
  height: 100%;
  max-width: 100vw;
  max-height: 100vh;
  aspect-ratio: 16 / 9;
  overflow: hidden;
  display: flex;
  align-items: center;
  justify-content: center;
  transform-style: preserve-3d;
  will-change: transform, opacity;
  box-shadow: 0 24px 60px rgba(0, 0, 0, 0.4);
}

.hero-video-element {
  width: 100%;
  height: 100%;
  object-fit: cover;
  object-position: center;
  display: block;
  pointer-events: none;
  border: none;
  outline: none;
}

/* Minimal Hero Welcome Headline */
.hero-welcome-container {
  position: absolute;
  inset: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 20;
  pointer-events: none;
  padding: 0 var(--container-padding);
  text-align: center;
  will-change: transform, opacity;
}

.hero-welcome-text {
  font-family: var(--font-main);
  font-size: clamp(2rem, 4.2vw, 3.75rem);
  font-weight: 500;
  letter-spacing: -0.025em;
  color: #FFFFFF;
  text-shadow: 0 4px 30px rgba(0, 0, 0, 0.7), 0 1px 4px rgba(0, 0, 0, 0.4);
  max-width: 900px;
  line-height: 1.15;
  opacity: 0;
  transform: translateY(12px) scale(0.98);
  transition: opacity 1.2s cubic-bezier(0.16, 1, 0.3, 1), transform 1.2s cubic-bezier(0.16, 1, 0.3, 1);
}

.hero-welcome-text.is-visible {
  opacity: 1;
  transform: translateY(0) scale(1);
}