:root {
  --bg-dark: #161618;
  --text-primary: #ffffff;
  --text-secondary: #a1a1a6;
  --accent-color: #0A84FF; /* Apple-like blue accent */
  --card-bg: #1c1c1e;
  --card-border: #2c2c2e;
  --success-color: #30d158;
  --danger-color: #ff453a;
}

body {
  background-color: var(--bg-dark);
  color: var(--text-primary);
  font-family: -apple-system, BlinkMacSystemFont, "SF Pro Display", "SF Pro Text", "Helvetica Neue", sans-serif;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  scroll-behavior: smooth;
  margin: 0;
  padding: 0;
  /* Replaced overflow-x: hidden with clip to prevent iOS scroll jank */
  overflow-x: clip; 
  /* Allow smooth vertical native scrolling */
  touch-action: pan-y; 
}

/* Glassmorphism utility */
.glass {
  background: rgba(28, 28, 30, 0.7);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border: 1px solid rgba(255, 255, 255, 0.08);
}

/* Disable heavy backdrop-filter on mobile to prevent severe scroll lag */
@media (max-width: 768px) {
  .glass {
    backdrop-filter: none;
    -webkit-backdrop-filter: none;
    background: rgba(28, 28, 30, 0.95); /* Make it more opaque to compensate for lack of blur */
  }
}

/* Card 3D Flip Setup */
.perspective-1000 {
  perspective: 1000px;
}

.transform-style-3d {
  transform-style: preserve-3d;
}

.backface-hidden {
  backface-visibility: hidden;
}

.flip-card-inner {
  position: relative;
  width: 100%;
  height: 100%;
  transition: transform 0.6s cubic-bezier(0.4, 0.2, 0.2, 1);
  transform-style: preserve-3d;
  /* Hardware acceleration for smooth flipping */
  will-change: transform;
}

.flip-card.flipped .flip-card-inner {
  transform: rotateY(180deg);
}

.flip-card-front, .flip-card-back {
  position: absolute;
  width: 100%;
  height: 100%;
  backface-visibility: hidden;
  border-radius: 1.5rem;
  padding: 2rem;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  text-align: center;
  background-color: var(--card-bg);
  border: 1px solid var(--card-border);
  box-shadow: 0 10px 30px rgba(0,0,0,0.3);
  /* Touch action optimization */
  touch-action: pan-y;
}

.flip-card-back {
  transform: rotateY(180deg);
}

/* Paper-turn scroll reveal */
.reveal-item {
  opacity: 0;
  transform: translateY(40px) rotateX(-10deg);
  transform-origin: top center;
  transition: opacity 0.8s ease-out, transform 0.8s cubic-bezier(0.175, 0.885, 0.32, 1.275);
  /* Hardware acceleration for scroll animations */
  will-change: transform, opacity;
}

.reveal-item.is-visible {
  opacity: 1;
  transform: translateY(0) rotateX(0deg);
}

/* Scrollbar customization */
::-webkit-scrollbar {
  width: 8px;
}

::-webkit-scrollbar-track {
  background: var(--bg-dark);
}

::-webkit-scrollbar-thumb {
  background: var(--card-border);
  border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
  background: var(--text-secondary);
}

/* Base button animations */
button {
  transition: transform 0.1s ease-in-out, background-color 0.2s ease, opacity 0.2s ease;
}

button:active {
  transform: scale(0.97);
}

.nav-tab.active {
  color: var(--text-primary);
  background-color: rgba(255, 255, 255, 0.1);
}

/* Floating Top Anchor */
#top-anchor {
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.3s ease;
  will-change: opacity;
}

#top-anchor.visible {
  opacity: 1;
  pointer-events: auto;
}