/* =============================================================
   基础层 (Base) —— 重置、排版、氛围背景、焦点与降级动效
   ============================================================= */

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

html { scroll-behavior: smooth; -webkit-text-size-adjust: 100%; }

body {
  font-family: var(--font-body);
  background: var(--color-bg);
  color: var(--color-text);
  line-height: 1.7;
  font-size: 16px;
  letter-spacing: .01em;
  overflow-x: hidden;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
  position: relative;
}

/* ---- 氛围层：深空蓝渐变网格 + 双色辉光 + 蓝图网格 ---- */
body::before {
  content: "";
  position: fixed;
  inset: 0;
  z-index: -2;
  pointer-events: none;
  background:
    radial-gradient(60rem 42rem at 12% -8%, var(--glow-1), transparent 60%),
    radial-gradient(54rem 40rem at 100% 4%, var(--glow-2), transparent 55%),
    radial-gradient(48rem 48rem at 50% 120%, var(--glow-3), transparent 60%),
    var(--color-bg);
}
/* 蓝图细网格 */
body::after {
  content: "";
  position: fixed;
  inset: 0;
  z-index: -1;
  pointer-events: none;
  opacity: .5;
  background-image:
    linear-gradient(var(--grid-line) 1px, transparent 1px),
    linear-gradient(90deg, var(--grid-line) 1px, transparent 1px);
  background-size: 56px 56px;
  -webkit-mask-image: radial-gradient(circle at 50% 30%, #000 0%, transparent 78%);
          mask-image: radial-gradient(circle at 50% 30%, #000 0%, transparent 78%);
}

/* ---- 颗粒噪点（轻微，叠加质感）---- */
.grain::after {
  content: "";
  position: fixed; inset: 0; z-index: 1; pointer-events: none;
  opacity: .045; mix-blend-mode: overlay;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg'%3E%3Cfilter id='n'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='.85' numOctaves='2'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23n)'/%3E%3C/svg%3E");
}

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

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

button { font-family: inherit; cursor: pointer; }

/* ---- 排版基线 ---- */
h1, h2, h3, h4 {
  font-family: var(--font-display);
  font-weight: 700;
  line-height: 1.06;
  letter-spacing: -.02em;
  color: var(--color-text);
}
h2 { font-size: clamp(28px, 4vw, 46px); }
h3 { font-size: clamp(18px, 2vw, 22px); letter-spacing: -.01em; }

p { color: var(--color-muted); }

.container {
  width: 100%;
  max-width: var(--maxw);
  margin-inline: auto;
  padding-inline: clamp(20px, 5vw, 40px);
}

.section { padding-block: clamp(64px, 9vw, 120px); position: relative; }

/* 段落小标题（眉题）*/
.eyebrow {
  font-family: var(--font-display);
  font-size: 13px;
  font-weight: 600;
  letter-spacing: .22em;
  text-transform: uppercase;
  color: var(--color-accent);
  display: inline-flex;
  align-items: center;
  gap: 10px;
}
.eyebrow::before {
  content: "";
  width: 26px; height: 1.5px;
  background: linear-gradient(90deg, var(--color-accent), transparent);
}

.section-head { max-width: 760px; margin-bottom: var(--space-6); }
.section-head h2 { margin-top: var(--space-3); }
.section-head p { margin-top: var(--space-3); font-size: 17px; }

/* 文本强调 */
.accent { color: var(--color-accent); }
.cyan   { color: var(--color-cyan); }

/* ---- 焦点可见（可访问性，2px + 偏移）---- */
:focus-visible {
  outline: 2px solid var(--color-accent);
  outline-offset: 3px;
  border-radius: 4px;
}

/* ---- 入场动画基础类 ----
   注意：只有 html.js（脚本可用）存在时才隐藏元素。
   脚本失效 / 首帧渲染时元素直接可见，避免整屏空白被视为“黑屏”。
   位移与时长都压得比较克制：快速滚动时不会出现整屏空白的观感。 */
.js .reveal { opacity: 0; transform: translateY(10px); }
.js .reveal.in {
  opacity: 1; transform: none;
  transition: opacity 150ms var(--ease-out),
              transform 150ms var(--ease-out);
}

/* ---- 无刷新切页（header/footer 常驻，仅 main 内容替换）---- */
#mainContent { display: block; }

/* 切页瞬间：淡出旧内容（只做透明度，不产生新的定位包含块）*/
.main-leaving {
  opacity: 0 !important;
  transition: opacity 130ms ease !important;
  pointer-events: none;
}
/* 新内容进入：轻微上浮 + 淡入，绝不出现纯黑/纯白空帧 */
.main-entering {
  animation: mainEnter 300ms var(--ease-out) both;
}
@keyframes mainEnter {
  from { opacity: 0; transform: translateY(8px); }
  to   { opacity: 1; transform: none; }
}

/* 顶部加载进度条（无刷新切页时提示，而非黑屏）*/
.nav-progress {
  position: fixed; top: 0; left: 0; z-index: 999;
  height: 2px; width: 0;
  background: linear-gradient(90deg, var(--color-accent), var(--color-cyan));
  box-shadow: 0 0 12px rgba(30,127,232,.55);
  opacity: 0;
  transition: width 320ms var(--ease-out), opacity 200ms linear;
  pointer-events: none;
}
.nav-progress.on { opacity: 1; }
.nav-progress.done { width: 100% !important; opacity: 0; transition: width 160ms ease, opacity 240ms linear 120ms; }

/* ---- 降级动效：尊重 prefers-reduced-motion ---- */
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  .reveal, .reveal.in { opacity: 1 !important; transform: none !important; transition: none !important; }
  *, *::before, *::after { animation-duration: .001ms !important; animation-iteration-count: 1 !important; transition-duration: .001ms !important; }
}

/* 选中态 */
::selection { background: rgba(30,127,232,.32); color: var(--color-selection); }

/* 滚动条（桌面）*/
::-webkit-scrollbar { width: 10px; height: 10px; }
::-webkit-scrollbar-track { background: var(--color-bg); }
::-webkit-scrollbar-thumb { background: var(--color-surface-3); border-radius: 99px; }
::-webkit-scrollbar-thumb:hover { background: var(--color-accent-strong); }