/* ===== 品牌与设计系统 ===== */
:root {
  /* Brand */
  --brand-primary: #002fa7;
  --brand-primary-light: #3b6de8;
  --brand-primary-muted: #e8f0fe;
  --kktong-accent: #3b82c0;

  /* Light theme neutrals */
  --bg-primary: #ffffff;
  --bg-secondary: #f8fafc;
  --bg-tertiary: #f1f5f9;
  --text-primary: #0f172a;
  --text-secondary: #475569;
  --text-muted: #94a3b8;

  /* Functional */
  --accent: #002fa7;
  --accent-light: #3b6de8;
  --border-light: #e2e8f0;
  --border-medium: #cbd5e1;
  --shadow-soft: 0 4px 20px rgba(0, 47, 167, 0.08);
  --shadow-medium: 0 8px 30px rgba(0, 47, 167, 0.12);

  /* Typography */
  --font:
    "Inter", -apple-system, BlinkMacSystemFont, "PingFang SC",
    "Microsoft YaHei", sans-serif;
  --tracking-tight: -0.03em;
  --tracking-tighter: -0.05em;

  /* Easing */
  --ease-out: cubic-bezier(0.16, 1, 0.3, 1);
  --ease-in-out: cubic-bezier(0.65, 0, 0.35, 1);
}

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

html {
  font-size: 16px;
  scroll-behavior: auto;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  font-family: var(--font);
  background: var(--bg-primary);
  color: var(--text-primary);
  overflow-x: hidden;
  line-height: 1.6;
}

body.is-loading {
  overflow: hidden;
}

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

em {
  font-style: italic;
  color: var(--brand-primary-light);
}

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

.container {
  width: 100%;
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 2rem;
}

.accent {
  color: var(--accent);
}

/* ===== Button ===== */
.btn {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.9rem 2rem;
  font-size: 0.9rem;
  font-weight: 600;
  letter-spacing: 0.02em;
  border: none;
  border-radius: 100px;
  background: var(--accent);
  color: #fff;
  transition: all 0.4s var(--ease-out);
  cursor: pointer;
  box-shadow: 0 4px 14px rgba(0, 47, 167, 0.25);
}

.btn:hover {
  background: var(--accent-light);
  transform: translateY(-2px);
  box-shadow: 0 8px 24px rgba(0, 47, 167, 0.3);
  gap: 0.85rem;
}

.btn__arrow {
  transition: transform 0.4s var(--ease-out);
}

.btn:hover .btn__arrow {
  transform: translateX(4px);
}

/* Section headings shared styles */
.section__heading {
  font-size: clamp(2rem, 4vw, 3rem);
  font-weight: 800;
  margin-bottom: 1rem;
  letter-spacing: var(--tracking-tight);
  color: var(--text-primary);
}

.section__heading-line {
  display: inline-block;
  position: relative;
}

.section__subheading {
  font-size: 1.1rem;
  color: var(--text-secondary);
  max-width: 600px;
  margin: 0 auto;
}

/* Defer rendering for below-the-fold sections */
.services,
.about,
.footer {
  content-visibility: auto;
  contain-intrinsic-size: auto 500px;
}

/* ===== Responsive base ===== */
@media (max-width: 768px) {
  .container {
    padding: 0 1.25rem;
  }

  .section__heading {
    font-size: clamp(1.75rem, 3.5vw, 2.5rem);
  }
}