:root {
  /* Google / Firebase Color Palette */
  --bg-primary: #f8f9fa; /* Light grey background */
  --bg-secondary: #ffffff; /* White cards */
  --border-subtle: #dadce0; /* Google subtle border */
  --border-medium: #bdc1c6;

  --text-primary: #202124; /* Google dark grey */
  --text-secondary: #5f6368; /* Google medium grey */
  --text-tertiary: #80868b;
  
  --accent-blue: #1a73e8; /* Google Blue */
  --accent-blue-hover: #1557b0;
  --firebase-orange: #f6820c;
  --firebase-yellow: #ffc400;

  --container-max: 1000px;
  --container-px: 2rem;
  --section-py: 5rem;
  
  --radius-sm: 4px;
  --radius-md: 8px; /* Classic Material card radius */
  --radius-lg: 24px;
  --radius-pill: 100px;
  
  --shadow-sm: 0 1px 2px 0 rgba(60,64,67,0.3), 0 1px 3px 1px rgba(60,64,67,0.15);
  --shadow-hover: 0 1px 3px 0 rgba(60,64,67,0.3), 0 4px 8px 3px rgba(60,64,67,0.15);
  
  --ease: cubic-bezier(0.4, 0, 0.2, 1);
  --font-en: "Google Sans", "Roboto", "Inter", -apple-system, sans-serif;
  --font-zh: "Noto Sans SC", "PingFang SC", sans-serif;
}

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

body {
  font-family: var(--font-en);
  background-color: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}

[data-lang="zh"] body { font-family: var(--font-zh); }
a { text-decoration: none; color: inherit; }

.container {
  max-width: var(--container-max);
  margin: 0 auto;
  padding-inline: var(--container-px);
}

/* ─── Navigation ─── */
#main-nav {
  position: fixed;
  top: 0; left: 0; width: 100%;
  height: 64px;
  background-color: var(--bg-secondary);
  border-bottom: 1px solid var(--border-subtle);
  display: flex; justify-content: space-between; align-items: center;
  padding: 0 2rem; z-index: 1000;
}

.logo {
  display: flex; align-items: center; gap: 0.5rem;
  font-weight: 500; font-size: 1.125rem; color: var(--text-primary);
}
.logo img { height: 24px; width: auto; }

.nav-links { display: flex; align-items: center; gap: 2rem; }
.nav-link {
  font-size: 0.875rem; font-weight: 500; color: var(--text-secondary);
  transition: color 0.2s var(--ease);
}
.nav-link:hover { color: var(--text-primary); }

.lang-btn {
  background: transparent;
  border: 1px solid var(--border-subtle);
  color: var(--accent-blue);
  padding: 0.35rem 1rem;
  border-radius: var(--radius-sm);
  font-size: 0.875rem; font-weight: 500;
  cursor: pointer; display: flex; align-items: center; gap: 0.5rem;
  transition: all 0.2s var(--ease);
}
.lang-btn:hover { background-color: rgba(26, 115, 232, 0.04); }

.mobile-menu-btn { display: none; }

/* ─── Hero ─── */
.hero {
  min-height: 80vh;
  display: flex; flex-direction: column; justify-content: center; align-items: center;
  text-align: center; padding: 8rem 2rem 4rem;
}
.hero h1 {
  font-size: clamp(2.5rem, 5vw, 3.5rem);
  font-weight: 400; line-height: 1.2; letter-spacing: -0.02em;
  margin-bottom: 1.5rem; color: var(--text-primary);
}
.hero-gradient {
  background: linear-gradient(90deg, var(--firebase-orange) 0%, var(--firebase-yellow) 100%);
  -webkit-background-clip: text; -webkit-text-fill-color: transparent;
  font-weight: 500;
}
.hero-sub {
  font-size: 1.125rem; color: var(--text-secondary); max-width: 600px;
  margin: 0 auto 2.5rem; font-weight: 400;
}
.hero-actions { display: flex; gap: 1rem; justify-content: center; }

/* ─── Buttons ─── */
.btn {
  padding: 0.6rem 1.5rem; border-radius: var(--radius-sm);
  font-weight: 500; font-size: 0.875rem; cursor: pointer;
  transition: background-color 0.2s var(--ease), box-shadow 0.2s var(--ease);
  border: none;
}
.btn-primary {
  background-color: var(--accent-blue); color: white;
}
.btn-primary:hover {
  background-color: var(--accent-blue-hover); box-shadow: var(--shadow-sm);
}
.btn-ghost {
  background-color: transparent; color: var(--accent-blue);
  border: 1px solid var(--border-subtle);
}
.btn-ghost:hover { background-color: rgba(26, 115, 232, 0.04); }

/* ─── Sections ─── */
.section { padding-block: 4rem; }
.section-header { text-align: center; margin-bottom: 3rem; }
.section-tag {
  display: inline-flex; align-items: center; gap: 0.5rem;
  font-size: 0.875rem; font-weight: 500; color: var(--firebase-orange);
  margin-bottom: 0.5rem; text-transform: uppercase;
}
.section-header h2 {
  font-size: 2rem; font-weight: 400; color: var(--text-primary);
}

/* ─── Services ─── */
.services-grid {
  display: grid; grid-template-columns: repeat(auto-fit, minmax(280px, 1fr)); gap: 1.5rem;
}
.service-card {
  padding: 1.5rem; border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md); background-color: var(--bg-secondary);
  transition: box-shadow 0.2s var(--ease), border-color 0.2s var(--ease);
  text-align: left;
}
.service-card:hover {
  box-shadow: var(--shadow-sm); border-color: var(--border-medium);
}
.service-icon-wrap { margin-bottom: 1rem; }
.service-icon {
  font-size: 1.5rem;
  background-color: rgba(26, 115, 232, 0.1); width: 40px; height: 40px;
  display: flex; align-items: center; justify-content: center;
  border-radius: var(--radius-md);
}
.service-card h3 {
  font-size: 1rem; font-weight: 500; margin-bottom: 0.5rem; color: var(--text-primary);
}
.service-card p { font-size: 0.875rem; color: var(--text-secondary); }

/* ─── About ─── */
.about {
  background-color: var(--bg-secondary);
  border-top: 1px solid var(--border-subtle);
  border-bottom: 1px solid var(--border-subtle);
}
.about-content { max-width: 800px; margin: 0 auto; text-align: center; }
.about-card p { font-size: 0.95rem; color: var(--text-secondary); }

/* ─── Contact ─── */
.contact-grid {
  display: grid; grid-template-columns: repeat(auto-fit, minmax(250px, 1fr)); gap: 1.5rem;
}
.contact-card {
  padding: 1.5rem; border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md); background-color: var(--bg-secondary);
  text-align: center;
}
.contact-icon {
  font-size: 1.25rem; color: var(--accent-blue); margin-bottom: 0.5rem;
}
.contact-card h3 {
  font-size: 0.875rem; font-weight: 500; color: var(--text-primary); margin-bottom: 0.5rem;
}
.contact-card a, .contact-card p {
  font-size: 0.875rem; color: var(--text-secondary);
}
.contact-card a:hover { color: var(--accent-blue); text-decoration: underline; }

/* ─── Footer ─── */
.footer {
  text-align: center; padding: 2rem; border-top: 1px solid var(--border-subtle);
  color: var(--text-tertiary); font-size: 0.75rem; background: var(--bg-primary);
}
.footer-links { display: flex; justify-content: center; gap: 1rem; margin-bottom: 1rem;}
.footer-links a:hover { color: var(--text-primary); }

@media (max-width: 768px) {
  .nav-links { display: none; }
  .hero { padding: 6rem 1.5rem 3rem; }
}