/* ===========================
   YUBAI LIN PORTFOLIO
   Main Stylesheet
   =========================== */

:root {
  --bg: #0f0f0e;
  --bg2: #141413;
  --bg3: #1a1a18;
  --ink: #e8e4dc;
  --ink-dim: #9a9690;
  --ink-faint: #4a4845;
  --accent: #c4b89a;
  --accent2: #8fa08a;
  --warm: #d4c4a0;
  --cool: #7a8fa0;
  --paper: #f0ead8;
  --tape: #c8b87a;

  --f-body: 'Noto Serif SC', 'Georgia', serif;
  --f-sans: 'Inter', 'Helvetica Neue', sans-serif;
  --f-mono: 'JetBrains Mono', 'Courier New', monospace;

  --gap: clamp(1rem, 3vw, 2rem);
  --section-gap: clamp(4rem, 10vw, 8rem);
}

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

html {
  scroll-behavior: smooth;
  font-size: 16px;
}

body {
  background: var(--bg);
  color: var(--ink);
  font-family: var(--f-body);
  line-height: 1.7;
  overflow-x: hidden;
  -webkit-font-smoothing: antialiased;
}

a {
  color: inherit;
  text-decoration: none;
}

img {
  max-width: 100%;
  display: block;
}

/* ===== NOISE OVERLAY ===== */
body::before {
  content: '';
  position: fixed;
  inset: 0;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='300' height='300'%3E%3Cfilter id='n'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.9' numOctaves='4' stitchTiles='stitch'/%3E%3CfeColorMatrix type='saturate' values='0'/%3E%3C/filter%3E%3Crect width='300' height='300' filter='url(%23n)' opacity='0.035'/%3E%3C/svg%3E");
  pointer-events: none;
  z-index: 9999;
  opacity: 0.4;
}

/* ===== TYPOGRAPHY ===== */
h1, h2, h3, h4 {
  font-family: var(--f-sans);
  font-weight: 400;
  letter-spacing: -0.02em;
  line-height: 1.2;
}

.mono {
  font-family: var(--f-mono);
  font-size: 0.75em;
  letter-spacing: 0.05em;
}

/* ===== NAVIGATION ===== */
.nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 100;
  padding: 1.25rem var(--gap);
  display: flex;
  align-items: center;
  justify-content: space-between;
  mix-blend-mode: normal;
  transition: background 0.3s;
}

.nav.scrolled {
  background: rgba(15, 15, 14, 0.92);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid rgba(255,255,255,0.04);
}

.nav-logo {
  font-family: var(--f-sans);
  font-size: 0.875rem;
  letter-spacing: 0.08em;
  color: var(--ink);
  text-transform: uppercase;
}

.nav-links {
  display: flex;
  gap: 2rem;
  list-style: none;
}

.nav-links a {
  font-family: var(--f-sans);
  font-size: 0.8125rem;
  color: var(--ink-dim);
  letter-spacing: 0.04em;
  transition: color 0.2s;
}

.nav-links a:hover {
  color: var(--ink);
}

/* Mobile nav toggle */
.nav-toggle {
  display: none;
  flex-direction: column;
  gap: 5px;
  cursor: pointer;
  padding: 4px;
  background: none;
  border: none;
}

.nav-toggle span {
  display: block;
  width: 22px;
  height: 1px;
  background: var(--ink);
  transition: all 0.3s;
}

/* ===== LAYOUT UTILITIES ===== */
.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 var(--gap);
}

.grid-2 { display: grid; grid-template-columns: 1fr 1fr; gap: var(--gap); }
.grid-3 { display: grid; grid-template-columns: repeat(3, 1fr); gap: var(--gap); }

.spacer { height: var(--section-gap); }
.spacer-sm { height: calc(var(--section-gap) * 0.5); }

/* ===== SECTION LABEL ===== */
.section-label {
  font-family: var(--f-mono);
  font-size: 0.6875rem;
  letter-spacing: 0.15em;
  color: var(--ink-faint);
  text-transform: uppercase;
  margin-bottom: 0.5rem;
}

/* ===== DIVIDER ===== */
.divider {
  width: 100%;
  height: 1px;
  background: rgba(255,255,255,0.06);
  margin: 3rem 0;
}

/* ===== SCROLL INDICATOR ===== */
.scroll-hint {
  position: absolute;
  bottom: 2rem;
  left: 50%;
  transform: translateX(-50%);
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.5rem;
}

.scroll-hint span {
  font-family: var(--f-mono);
  font-size: 0.625rem;
  letter-spacing: 0.12em;
  color: var(--ink-faint);
  text-transform: uppercase;
}

.scroll-line {
  width: 1px;
  height: 40px;
  background: linear-gradient(to bottom, transparent, var(--ink-faint));
  animation: scrollLine 2s ease infinite;
}

@keyframes scrollLine {
  0% { transform: scaleY(0); transform-origin: top; }
  50% { transform: scaleY(1); transform-origin: top; }
  51% { transform: scaleY(1); transform-origin: bottom; }
  100% { transform: scaleY(0); transform-origin: bottom; }
}

/* ===== PROJECT PAGE BASE ===== */
.project-back {
  position: fixed;
  top: 1.25rem;
  left: var(--gap);
  z-index: 200;
  font-family: var(--f-mono);
  font-size: 0.6875rem;
  letter-spacing: 0.1em;
  color: var(--ink-dim);
  display: flex;
  align-items: center;
  gap: 0.5rem;
  transition: color 0.2s;
}

.project-back:hover {
  color: var(--ink);
}

.project-back::before {
  content: '←';
}

/* ===== ABOUT PAGE ===== */
.about-header {
  min-height: 50vh;
  display: flex;
  align-items: flex-end;
  padding: 8rem var(--gap) 4rem;
}

/* ===== TAG / BADGE ===== */
.tag {
  display: inline-block;
  font-family: var(--f-mono);
  font-size: 0.625rem;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  padding: 0.25rem 0.625rem;
  border: 1px solid rgba(255,255,255,0.12);
  color: var(--ink-dim);
  margin: 0.2rem;
}

/* ===== RESPONSIVE ===== */
@media (max-width: 768px) {
  .nav-links {
    display: none;
    position: fixed;
    inset: 0;
    background: rgba(15,15,14,0.97);
    flex-direction: column;
    align-items: center;
    justify-content: center;
    gap: 2.5rem;
    z-index: 99;
  }
  .nav-links.open {
    display: flex;
  }
  .nav-links a {
    font-size: 1.25rem;
    letter-spacing: 0.1em;
  }
  .nav-toggle {
    display: flex;
    z-index: 200;
  }
  .grid-2, .grid-3 {
    grid-template-columns: 1fr;
  }
}