/* =====================================================================
 * bienac — Khoa học huyền ảo
 * ===================================================================== */
:root {
  --cyan: #1ee3e3;
  --mint: #7df9d4;
  --violet: #9a6bff;
  --ink: #050a14;
  --text: #e8f4f6;
  --text-dim: #9fb6c0;
  --glass: rgba(10, 22, 34, 0.55);
  --glass-border: rgba(30, 227, 227, 0.18);
  --radius: 18px;
  --font: 'Be Vietnam Pro', system-ui, -apple-system, sans-serif;
}

* { margin: 0; padding: 0; box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  font-family: var(--font);
  background: var(--ink);
  color: var(--text);
  overflow-x: hidden;
  -webkit-font-smoothing: antialiased;
}

/* ------------------------------------------------- Nền hiệu ứng -- */
#fx-canvas {
  position: fixed;
  inset: 0;
  width: 100vw;
  height: 100vh;
  z-index: -2;
  opacity: 1;
  transition: opacity 0.35s ease;
}
#fx-canvas.fx-fading { opacity: 0; }

.no-webgl {
  background:
    radial-gradient(1200px 600px at 70% 10%, rgba(30, 227, 227, 0.12), transparent),
    radial-gradient(900px 500px at 20% 80%, rgba(154, 107, 255, 0.12), transparent),
    var(--ink);
}

.vignette {
  position: fixed;
  inset: 0;
  z-index: -1;
  pointer-events: none;
  background:
    radial-gradient(ellipse at center, transparent 55%, rgba(3, 6, 12, 0.55) 100%);
}

/* ------------------------------------------------------- Header -- */
.site-header {
  position: fixed;
  top: 0; left: 0; right: 0;
  z-index: 50;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 18px clamp(20px, 5vw, 56px);
  transition: background 0.3s ease, backdrop-filter 0.3s ease, box-shadow 0.3s ease;
}
.site-header.scrolled {
  background: rgba(5, 10, 20, 0.7);
  backdrop-filter: blur(14px);
  -webkit-backdrop-filter: blur(14px);
  box-shadow: 0 1px 0 rgba(30, 227, 227, 0.12);
}

.brand {
  display: flex;
  align-items: center;
  gap: 12px;
  text-decoration: none;
  color: var(--text);
}
.brand-logo img {
  width: 38px;
  height: 38px;
  display: block;
  filter: drop-shadow(0 0 8px rgba(30, 227, 227, 0.55));
}
.brand-name {
  font-size: 1.35rem;
  font-weight: 800;
  letter-spacing: 0.02em;
  background: linear-gradient(90deg, var(--mint), var(--cyan));
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
}

.site-nav {
  display: flex;
  align-items: center;
  gap: clamp(14px, 3vw, 30px);
}
.site-nav a {
  color: var(--text-dim);
  text-decoration: none;
  font-weight: 600;
  font-size: 0.95rem;
  transition: color 0.2s ease;
}
.site-nav a:hover { color: var(--cyan); }
.site-nav .nav-cta {
  color: var(--ink);
  background: linear-gradient(90deg, var(--mint), var(--cyan));
  padding: 9px 18px;
  border-radius: 999px;
  box-shadow: 0 0 18px rgba(30, 227, 227, 0.35);
  transition: transform 0.2s ease, box-shadow 0.2s ease;
}
.site-nav .nav-cta:hover {
  color: var(--ink);
  transform: translateY(-1px);
  box-shadow: 0 0 28px rgba(30, 227, 227, 0.55);
}

/* --------------------------------------------------------- Hero -- */
.hero {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  text-align: center;
  padding: 100px 20px 60px;
  position: relative;
}

.hero-logo img {
  width: clamp(110px, 16vw, 170px);
  height: auto;
  filter: drop-shadow(0 0 26px rgba(30, 227, 227, 0.6));
  animation: float 6s ease-in-out infinite;
}
@keyframes float {
  0%, 100% { transform: translateY(0) rotate(-2deg); }
  50%      { transform: translateY(-14px) rotate(2deg); }
}

.hero-title {
  margin-top: 18px;
  font-size: clamp(3.2rem, 10vw, 6.5rem);
  font-weight: 800;
  letter-spacing: 0.01em;
  line-height: 1;
  text-shadow: 0 0 40px rgba(30, 227, 227, 0.35);
}
.accent {
  background: linear-gradient(90deg, var(--mint), var(--cyan), var(--violet));
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
}

.hero-tagline {
  margin-top: 16px;
  font-size: clamp(1.1rem, 2.6vw, 1.5rem);
  font-weight: 300;
  color: var(--text);
}
.hero-sub {
  margin-top: 8px;
  font-size: 0.95rem;
  color: var(--text-dim);
  letter-spacing: 0.14em;
  text-transform: uppercase;
}

.hero-actions {
  margin-top: 36px;
  display: flex;
  gap: 16px;
  flex-wrap: wrap;
  justify-content: center;
}

.btn {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  padding: 14px 28px;
  border-radius: 999px;
  font-weight: 700;
  font-size: 1rem;
  text-decoration: none;
  transition: transform 0.2s ease, box-shadow 0.2s ease, background 0.2s ease;
}
.btn-primary {
  color: var(--ink);
  background: linear-gradient(90deg, var(--mint), var(--cyan));
  box-shadow: 0 0 24px rgba(30, 227, 227, 0.4);
}
.btn-primary:hover {
  transform: translateY(-2px) scale(1.02);
  box-shadow: 0 0 40px rgba(30, 227, 227, 0.65);
}
.btn-ghost {
  color: var(--text);
  border: 1px solid var(--glass-border);
  background: var(--glass);
  backdrop-filter: blur(10px);
  -webkit-backdrop-filter: blur(10px);
}
.btn-ghost:hover {
  border-color: rgba(30, 227, 227, 0.5);
  box-shadow: 0 0 20px rgba(30, 227, 227, 0.2);
  transform: translateY(-2px);
}

.scroll-hint {
  position: absolute;
  bottom: 28px;
  left: 50%;
  transform: translateX(-50%);
  width: 26px;
  height: 42px;
  border: 2px solid rgba(159, 182, 192, 0.5);
  border-radius: 14px;
}
.scroll-hint span {
  position: absolute;
  top: 7px;
  left: 50%;
  width: 4px;
  height: 8px;
  margin-left: -2px;
  border-radius: 2px;
  background: var(--cyan);
  animation: scrollhint 1.8s ease-in-out infinite;
}
@keyframes scrollhint {
  0%   { transform: translateY(0); opacity: 1; }
  70%  { transform: translateY(14px); opacity: 0; }
  100% { transform: translateY(0); opacity: 0; }
}

/* ----------------------------------------------------- Sections -- */
.section {
  max-width: 1120px;
  margin: 0 auto;
  padding: clamp(70px, 10vw, 120px) clamp(20px, 5vw, 40px);
  opacity: 0;
  transform: translateY(28px);
  transition: opacity 0.7s ease, transform 0.7s ease;
}
.section.visible { opacity: 1; transform: none; }

.section-title {
  font-size: clamp(1.9rem, 4.5vw, 2.8rem);
  font-weight: 800;
}
.section-sub {
  margin-top: 10px;
  color: var(--text-dim);
  font-size: 1.05rem;
}
.section-more { margin-top: 36px; text-align: center; }

/* -------------------------------------------------- Lưới video -- */
.video-grid {
  margin-top: 40px;
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 24px;
}

.video-card {
  display: block;
  text-decoration: none;
  color: var(--text);
  background: var(--glass);
  border: 1px solid var(--glass-border);
  border-radius: var(--radius);
  overflow: hidden;
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  transition: transform 0.3s ease, box-shadow 0.3s ease, border-color 0.3s ease,
              opacity 0.7s ease;
  opacity: 0;
  transform: translateY(24px);
}
.video-card.visible { opacity: 1; transform: none; }
.video-card:hover {
  transform: translateY(-6px);
  border-color: rgba(30, 227, 227, 0.45);
  box-shadow: 0 14px 40px rgba(0, 0, 0, 0.45), 0 0 24px rgba(30, 227, 227, 0.18);
}

.video-thumb {
  aspect-ratio: 16 / 9;
  display: flex;
  align-items: center;
  justify-content: center;
  position: relative;
  overflow: hidden;
}
.video-thumb img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  transition: transform 0.4s ease;
}
.video-card:hover .video-thumb img { transform: scale(1.06); }
.thumb-mark {
  font-size: 2.2rem;
  color: rgba(232, 244, 246, 0.85);
  text-shadow: 0 0 18px rgba(30, 227, 227, 0.8);
}

.video-meta { padding: 18px 20px 22px; }
.video-tag {
  display: inline-block;
  font-size: 0.75rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--cyan);
  background: rgba(30, 227, 227, 0.1);
  border: 1px solid rgba(30, 227, 227, 0.25);
  padding: 4px 10px;
  border-radius: 999px;
  margin-bottom: 10px;
}
.video-meta h3 {
  font-size: 1.08rem;
  font-weight: 600;
  line-height: 1.45;
}

/* -------------------------------------------------------- About -- */
.about-card {
  display: flex;
  gap: clamp(24px, 5vw, 56px);
  align-items: center;
  background: var(--glass);
  border: 1px solid var(--glass-border);
  border-radius: 28px;
  padding: clamp(28px, 5vw, 56px);
  backdrop-filter: blur(14px);
  -webkit-backdrop-filter: blur(14px);
}
.about-logo img {
  width: clamp(90px, 12vw, 150px);
  filter: drop-shadow(0 0 22px rgba(30, 227, 227, 0.5));
}
.about-text p {
  margin-top: 16px;
  color: var(--text-dim);
  line-height: 1.8;
  font-size: 1.02rem;
}
.about-text .btn { margin-top: 26px; }

@media (max-width: 720px) {
  .about-card { flex-direction: column; text-align: center; }
}

/* --------------------------------------- Bảng chọn hiệu ứng nền -- */
.fx-switcher {
  position: fixed;
  right: 22px;
  bottom: 22px;
  z-index: 60;
  display: flex;
  flex-direction: column;
  align-items: flex-end;
  gap: 10px;
}

.fx-toggle {
  width: 48px;
  height: 48px;
  border-radius: 50%;
  border: 1px solid var(--glass-border);
  background: var(--glass);
  color: var(--cyan);
  font-size: 1.3rem;
  cursor: pointer;
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  box-shadow: 0 0 18px rgba(30, 227, 227, 0.25);
  transition: transform 0.25s ease, box-shadow 0.25s ease;
}
.fx-toggle:hover {
  transform: rotate(20deg) scale(1.06);
  box-shadow: 0 0 28px rgba(30, 227, 227, 0.45);
}

.fx-options {
  display: flex;
  flex-direction: column;
  gap: 6px;
  padding: 14px;
  border-radius: var(--radius);
  border: 1px solid var(--glass-border);
  background: var(--glass);
  backdrop-filter: blur(14px);
  -webkit-backdrop-filter: blur(14px);
  transition: opacity 0.25s ease, transform 0.25s ease;
}
.fx-options.collapsed {
  opacity: 0;
  transform: translateY(8px);
  pointer-events: none;
}

.fx-label {
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--text-dim);
  padding: 0 4px 6px;
}

.fx-options button {
  font-family: var(--font);
  font-size: 0.92rem;
  font-weight: 600;
  text-align: left;
  color: var(--text-dim);
  background: transparent;
  border: 1px solid transparent;
  border-radius: 12px;
  padding: 9px 14px;
  cursor: pointer;
  transition: all 0.2s ease;
}
.fx-options button:hover {
  color: var(--text);
  background: rgba(30, 227, 227, 0.08);
}
.fx-options button.active {
  color: var(--cyan);
  background: rgba(30, 227, 227, 0.12);
  border-color: rgba(30, 227, 227, 0.35);
  box-shadow: 0 0 14px rgba(30, 227, 227, 0.2);
}

/* ------------------------------------------------------- Footer -- */
.site-footer {
  text-align: center;
  padding: 40px 20px 110px;
  color: var(--text-dim);
  font-size: 0.9rem;
}

/* --------------------------- FAB bong bóng hiện tượng vật lý ----- */
.phys-bubble {
  position: fixed;
  left: 0;
  top: 0;
  z-index: 70;
  width: 56px;
  height: 56px;
  padding: 0;
  border-radius: 50%;
  border: 1px solid rgba(154, 107, 255, 0.4);
  background:
    radial-gradient(circle at 30% 26%, rgba(255, 255, 255, 0.55), rgba(255, 255, 255, 0.05) 38%, transparent 60%),
    radial-gradient(circle at 72% 78%, rgba(30, 227, 227, 0.35), transparent 55%),
    rgba(22, 16, 48, 0.45);
  color: var(--text);
  cursor: grab;
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  box-shadow:
    0 0 26px rgba(154, 107, 255, 0.4),
    inset 0 0 16px rgba(255, 255, 255, 0.14);
  touch-action: none;
  user-select: none;
  -webkit-user-select: none;
  will-change: transform;
  transition: box-shadow 0.25s ease;
}
.phys-bubble:hover {
  box-shadow:
    0 0 38px rgba(154, 107, 255, 0.6),
    inset 0 0 18px rgba(255, 255, 255, 0.2);
}
.phys-bubble.grabbing { cursor: grabbing; }
.phys-bubble.open {
  box-shadow:
    0 0 42px rgba(30, 227, 227, 0.55),
    inset 0 0 18px rgba(255, 255, 255, 0.2);
}
.phys-icon {
  display: block;
  font-size: 1.6rem;
  line-height: 56px;
  text-shadow: 0 0 14px rgba(154, 107, 255, 0.9);
  animation: phys-spin 14s linear infinite;
}
@keyframes phys-spin {
  from { transform: rotate(0deg); }
  to   { transform: rotate(360deg); }
}

.phys-menu {
  position: fixed;
  left: 0;
  top: 0;
  z-index: 69;
  display: flex;
  flex-direction: column;
  gap: 6px;
  padding: 14px;
  border-radius: var(--radius);
  border: 1px solid rgba(154, 107, 255, 0.3);
  background: var(--glass);
  backdrop-filter: blur(14px);
  -webkit-backdrop-filter: blur(14px);
  box-shadow: 0 14px 44px rgba(0, 0, 0, 0.5), 0 0 26px rgba(154, 107, 255, 0.18);
  transition: opacity 0.22s ease;
  will-change: transform;
}
.phys-menu.collapsed {
  opacity: 0;
  pointer-events: none;
}
.phys-label {
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--text-dim);
  padding: 0 4px 6px;
}
.phys-menu button {
  font-family: var(--font);
  font-size: 0.92rem;
  font-weight: 600;
  text-align: left;
  color: var(--text-dim);
  background: transparent;
  border: 1px solid transparent;
  border-radius: 12px;
  padding: 9px 14px;
  cursor: pointer;
  transition: all 0.2s ease;
}
.phys-menu button:hover {
  color: var(--text);
  background: rgba(154, 107, 255, 0.1);
}
.phys-menu button.active {
  color: var(--violet);
  background: rgba(154, 107, 255, 0.14);
  border-color: rgba(154, 107, 255, 0.4);
  box-shadow: 0 0 14px rgba(154, 107, 255, 0.25);
}

/* -------------------------------------------------- Reduced motion */
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  .hero-logo img, .scroll-hint span, .phys-icon { animation: none; }
  .section, .video-card { transition: none; opacity: 1; transform: none; }
}