/* ============================================================
   base.css —— 重置、排版、布局工具、动效基础
   ============================================================ */

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

html {
  -webkit-text-size-adjust: 100%;
  scroll-behavior: smooth;
  scroll-padding-top: 96px;
}

body {
  margin: 0;
  font-family: var(--font-cn);
  font-size: var(--fs-body);
  line-height: 1.75;
  color: var(--t-1);
  background: var(--c-bg);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  overflow-x: hidden;
}

img, svg, video { display: block; max-width: 100%; }
img { height: auto; }

h1, h2, h3, h4, h5, h6 {
  margin: 0 0 .5em;
  font-weight: 700;
  line-height: 1.25;
  letter-spacing: -.01em;
  color: var(--t-1);
}
h1 { font-size: var(--fs-h1); }
h2 { font-size: var(--fs-h2); }
h3 { font-size: var(--fs-h3); }
h4 { font-size: var(--fs-h4); }
p { margin: 0 0 1em; }
p:last-child { margin-bottom: 0; }

a { color: var(--c-blue); text-decoration: none; transition: color var(--t-fast) var(--ease); }
a:hover { color: var(--c-blue-700); }

ul, ol { margin: 0; padding: 0; }
li { list-style: none; }

button { font: inherit; color: inherit; background: none; border: 0; cursor: pointer; }
input, textarea, select { font: inherit; color: inherit; }

::selection { background: rgba(26, 111, 212, .18); }

/* ---------- 焦点可见（无障碍） ---------- */
:focus-visible {
  outline: 2px solid var(--c-blue);
  outline-offset: 3px;
  border-radius: 4px;
}

/* ---------- 容器 ---------- */
.container {
  width: 100%;
  max-width: var(--container);
  margin: 0 auto;
  padding: 0 var(--sp-6);
}
.container--narrow { max-width: 960px; }

/* ---------- 区块 ---------- */
.section { padding: var(--section-y) 0; }
.section--soft { background: var(--c-bg-soft); }
.section--dark { background: var(--grad-dark); color: var(--t-on-dark); }
.section--dark h2, .section--dark h3 { color: var(--c-white); }

/* ---------- 区块标题 ---------- */
.sec-head { max-width: 760px; margin-bottom: var(--sp-7); }
.sec-head--center { margin-left: auto; margin-right: auto; text-align: center; }
.sec-kicker {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  font-size: var(--fs-xs);
  font-weight: 700;
  letter-spacing: .14em;
  text-transform: uppercase;
  color: var(--c-blue);
  margin-bottom: var(--sp-3);
}
.sec-kicker::before {
  content: "";
  width: 22px; height: 2px;
  border-radius: 2px;
  background: var(--grad-main);
}
.sec-head--center .sec-kicker::before { display: none; }
.sec-title { font-size: var(--fs-h2); font-weight: 800; margin-bottom: var(--sp-3); }
.sec-desc { font-size: var(--fs-lead); color: var(--t-2); margin: 0; }
.section--dark .sec-desc { color: var(--t-on-dark-2); }

/* ---------- 渐变文字 ---------- */
.grad-text {
  background: var(--grad-main);
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
  color: transparent;
}
.grad-text--tech {
  background: var(--grad-tech);
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
}

/* ---------- 工具类 ---------- */
.sr-only {
  position: absolute; width: 1px; height: 1px;
  padding: 0; margin: -1px; overflow: hidden;
  clip: rect(0 0 0 0); white-space: nowrap; border: 0;
}
.text-center { text-align: center; }
.mt-0 { margin-top: 0; }
.hide { display: none !important; }

/* ---------- 滚动进场动效 ---------- */
.reveal {
  opacity: 0;
  transform: translateY(18px);
  transition: opacity var(--t-slow) var(--ease-out),
              transform var(--t-slow) var(--ease-out);
  transition-delay: var(--d, 0ms);
  will-change: opacity, transform;
}
.reveal.is-in { opacity: 1; transform: none; }

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

/* ---------- 跳转到主内容 ---------- */
.skip-link {
  position: absolute; left: 50%; top: -60px;
  transform: translateX(-50%);
  z-index: 999;
  padding: 10px 20px;
  background: var(--c-blue);
  color: #fff;
  border-radius: 0 0 var(--r-md) var(--r-md);
  font-weight: 600;
  transition: top var(--t-mid) var(--ease);
}
.skip-link:focus { top: 0; color: #fff; }