/* ==========================================================================
   Nexora AI — Base Layer
   重置、排版基准、焦点可见性、降级动效、氛围层
   ========================================================================== */

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

html {
  -webkit-text-size-adjust: 100%;
  scroll-behavior: smooth;
  scroll-padding-top: calc(var(--header-h) + 1.5rem);
  /* 抑制横向溢出。放在 html 上而非 body，避免 body 形成滚动容器后破坏 sticky 定位 */
  overflow-x: hidden;
}

body {
  margin: 0;
  background-color: var(--color-bg);
  color: var(--color-text);
  font-family: var(--font-body);
  font-size: var(--fs-base);
  line-height: var(--lh-body);
  letter-spacing: var(--ls-normal);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

img, svg, video { display: block; max-width: 100%; }
a { color: inherit; text-decoration: none; }
button, input, select, textarea { font: inherit; color: inherit; }
ul, ol { margin: 0; padding: 0; list-style: none; }

/* ---------- 标题排印 ---------- */
h1, h2, h3, h4, h5, h6 {
  margin: 0;
  font-family: var(--font-display);
  font-weight: 700;
  line-height: var(--lh-snug);
  letter-spacing: var(--ls-tight);
  color: var(--color-text);
  text-wrap: balance;
}

h1 { font-size: clamp(2.25rem, 5.2vw, var(--fs-5xl)); line-height: var(--lh-tight); letter-spacing: var(--ls-display); }
h2 { font-size: clamp(1.75rem, 3.4vw, var(--fs-3xl)); letter-spacing: var(--ls-display); }
h3 { font-size: clamp(1.25rem, 2vw, var(--fs-xl)); }
h4 { font-size: var(--fs-lg); }

p { margin: 0 0 var(--space-3); }
p:last-child { margin-bottom: 0; }

strong { font-weight: 600; color: var(--color-text); }
em { font-style: normal; color: var(--color-accent); }

code, kbd, samp { font-family: var(--font-mono); font-size: 0.9em; }

/* ---------- 焦点可见性（键盘可达性，不可移除） ---------- */
:focus-visible {
  outline: 2px solid var(--color-accent);
  outline-offset: 2px;
  border-radius: var(--radius-xs);
}
:focus:not(:focus-visible) { outline: none; }

::selection { background: var(--color-accent); color: #04120f; }

/* ---------- 跳转链接（屏幕阅读器/键盘用户） ---------- */
.skip-link {
  position: absolute;
  top: -100px; left: var(--space-3);
  z-index: 200;
  padding: var(--space-2) var(--space-3);
  background: var(--color-accent);
  color: #04120f;
  font-family: var(--font-mono);
  font-size: var(--fs-xs);
  border-radius: var(--radius-sm);
}
.skip-link:focus { top: var(--space-3); }

/* ==========================================================================
   氛围层
   三层叠加：渐变网格（冷光晕） + 工程网格线 + 噪点颗粒
   全部 fixed 定位、pointer-events: none，不干扰交互
   ========================================================================== */

.atmosphere::before {
  content: "";
  position: fixed;
  inset: 0;
  z-index: 0;
  pointer-events: none;
  background:
    radial-gradient(52rem 34rem at 8% -8%,  rgba(47, 227, 196, 0.10), transparent 62%),
    radial-gradient(46rem 32rem at 98% 4%,   rgba(58, 122, 224, 0.10), transparent 58%),
    radial-gradient(40rem 30rem at 52% 108%, rgba(47, 227, 196, 0.05), transparent 60%);
}

/* 工程网格线：每 64px 一条，极低对比，制造"图纸/仪表"的基底感 */
.atmosphere::after {
  content: "";
  position: fixed;
  inset: 0;
  z-index: 0;
  pointer-events: none;
  opacity: 0.5;
  background-image:
    linear-gradient(to right,  rgba(230, 237, 246, 0.028) 1px, transparent 1px),
    linear-gradient(to bottom, rgba(230, 237, 246, 0.028) 1px, transparent 1px);
  background-size: 64px 64px;
  -webkit-mask-image: radial-gradient(ellipse 90% 70% at 50% 30%, #000 20%, transparent 92%);
  mask-image: radial-gradient(ellipse 90% 70% at 50% 30%, #000 20%, transparent 92%);
}

/* 噪点颗粒：SVG feTurbulence 生成的 data-URI，5% 透明度 */
.grain-layer {
  position: fixed;
  inset: 0;
  z-index: 1;
  pointer-events: none;
  opacity: 0.05;
  mix-blend-mode: overlay;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='240' height='240'%3E%3Cfilter id='n'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='.82' numOctaves='3'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23n)'/%3E%3C/svg%3E");
}

/* 内容层必须高于氛围层 */
.site-header, main, .site-footer { position: relative; z-index: 2; }

/* ==========================================================================
   滚动入场（一次编排的序列，靠 --i 变量错峰）
   ========================================================================== */
.reveal {
  opacity: 0;
  transform: translateY(22px);
}
.reveal.is-in {
  opacity: 1;
  transform: none;
  transition:
    opacity   var(--dur-slow) var(--ease-out),
    transform var(--dur-slow) var(--ease-out);
  transition-delay: calc(var(--i, 0) * 80ms);
}

/* ---------- 降级：尊重系统减弱动效偏好 ---------- */
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
  .reveal { opacity: 1 !important; transform: none !important; }
}

/* ---------- 打印 ---------- */
@media print {
  .atmosphere::before, .atmosphere::after, .grain-layer, .site-header { display: none; }
  body { background: #fff; color: #000; }
}