:root {
  /* Colors */
  --color-bg: #ffffff;
  --color-text: #1a1a1a;
  --color-text-secondary: #666666;
  --color-text-muted: #999999;
  --avatar-bg: #f1f1f1;

  --accent-green: #10b981;
  --accent-yellow: #f59e0b;
  --accent-blue: #3b82f6;

  --gray-100: #f5f5f5;
  --gray-200: #e5e5e5;
  --gray-300: #d4d4d4;
  --gray-400: #a3a3a3;
  --border: #e5e5e5;

  /* Typography */
  --ff-primary: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  --ff-fallback: Arial, sans-serif;
  --fs-xs: 0.75rem;
  --fs-sm: 0.875rem;
  --fs-base: 1rem;
  --fs-lg: 1.125rem;
  --fs-xl: 1.25rem;
  --fs-2xl: 1.5rem;
  --fs-3xl: 1.875rem;
  --fs-4xl: 2.25rem;
  --fw-normal: 400;
  --fw-medium: 500;
  --fw-semibold: 600;
  --fw-bold: 700;
  --lh-tight: 1.25;
  --lh-normal: 1.5;
  --lh-relaxed: 1.75;

  /* Spacing */
  --sp-xs: 0.5rem;
  --sp-sm: 0.75rem;
  --sp-md: 1rem;
  --sp-lg: 1.5rem;
  --sp-xl: 2rem;
  --sp-2xl: 3rem;
  --sp-3xl: 4rem;
  --sp-4xl: 6rem;

  /* Layout */
  --max-w: 1200px;
  --container-px: 1rem;
  --section-space: 4rem;
  --grid-gap: 1.5rem;

  /* Effects */
  --transition: 180ms ease-in-out;
}

/* Dark theme */
[data-theme="dark"] {
  --color-bg: #0b0b0b;
  --color-text: #ededed;
  --color-text-secondary: #bdbdbd;
  --color-text-muted: #9aa0a6;
  --gray-100: #111111;
  --gray-200: #1a1a1a;
  --gray-300: #2a2a2a;
  --gray-400: #6b7280;
  --border: #262626;
  --avatar-bg: #0F0F0F;
}

/* Base */
* { box-sizing: border-box; }
html, body { height: 100%; }
body {
  margin: 0;
  font-family: var(--ff-primary), var(--ff-fallback);
  color: var(--color-text);
  background: var(--color-bg);
  line-height: var(--lh-normal);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

.skip-link {
  position: absolute;
  left: -9999px;
}
.skip-link:focus { left: 1rem; top: 1rem; background: var(--gray-100); padding: var(--sp-xs) var(--sp-sm); border-radius: 6px; }

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

.section { padding: var(--section-space) 0; }
.section-title {
  font-size: var(--fs-2xl);
  font-weight: var(--fw-bold);
  margin: 0 0 var(--sp-xl);
}

/* Navigation */
.site-header { position: sticky; top: 0; backdrop-filter: saturate(180%) blur(10px); }
.nav {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: var(--sp-lg);
  padding: var(--sp-md) 0;
}
.nav-list {
  display: flex;
  gap: var(--sp-lg);
  list-style: none;
  margin: 0;
  padding: 0;
}
.nav-link {
  color: var(--color-text-muted);
  font-size: var(--fs-sm);
  font-weight: var(--fw-medium);
  text-decoration: none;
  transition: color var(--transition);
}
.nav-link:hover, .nav-link:focus { color: var(--color-text); }
.icon-button {
  margin-left: auto;
  background: transparent;
  border: 1px solid var(--border);
  color: var(--color-text);
  border-radius: 8px;
  padding: 0.4rem;
  cursor: pointer;
}
.icon { width: 20px; height: 20px; fill: currentColor; display: block; }
.icon-moon, .icon-sun { width: 20px; height: 20px; }
[data-theme="dark"] .icon-moon { display: none; }
[data-theme="dark"] .icon-sun { display: inline; }
.icon-sun { display: none; }
.icon-moon { display: inline; }

/* Hero */
.hero {
  display: grid;
  grid-template-columns: 1fr auto;
  align-items: center;
  gap: var(--grid-gap);
}
.hero-title { font-size: var(--fs-4xl); font-weight: var(--fw-bold); margin: 0 0 var(--sp-sm); }
.hero-subtitle { font-size: var(--fs-lg); color: var(--color-text-secondary); margin: 0; max-width: 60ch; }
.hero-avatar { width: 10rem; height: 10rem; border-radius: 999px; object-fit: cover; background-color: var(--avatar-bg); }
.contact-line { display: flex; align-items: center; gap: 0.75rem; flex-wrap: wrap; }
.icon-link { display: inline-flex; align-items: center; justify-content: center; width: 34px; height: 34px; border: 1px solid var(--border); border-radius: 8px; color: var(--color-text); text-decoration: none; transition: background var(--transition), transform var(--transition); }
.icon-link:hover { background: var(--gray-100); transform: translateY(-1px); }
[data-theme="dark"] .icon-link:hover { background: var(--gray-200); }

/* Grid Cards */
.grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(300px, 1fr)); gap: var(--grid-gap); }
.card {
  background: #f1f1f1;
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: var(--sp-xl);
  transition: transform var(--transition), box-shadow var(--transition);
}
[data-theme="dark"] .card { background: #0f0f0f; }
.card:hover { transform: translateY(-4px); }
.card-title { font-size: var(--fs-lg); font-weight: var(--fw-semibold); margin: 0 0 var(--sp-sm); }
.card-desc { font-size: var(--fs-sm); color: var(--color-text-secondary); margin: 0 0 var(--sp-sm); line-height: var(--lh-relaxed); }
.card-meta { font-size: var(--fs-xs); color: var(--color-text-muted); }

.featured { position: relative; }
.bordered-accent-blue { border-top: 3px solid var(--accent-blue); }
.bordered-accent-green { border-top: 3px solid var(--accent-green); }
.bordered-accent-yellow { border-top: 3px solid var(--accent-yellow); }

/* Card media */
.card-media {
  aspect-ratio: 16 / 9;
  background: var(--gray-100);
  border: 1px solid var(--border);
  border-radius: 8px;
  overflow: hidden;
  margin: 0 0 var(--sp-md);
}
[data-theme="dark"] .card-media { background: var(--gray-200); }
.card-media img { width: 100%; height: 100%; object-fit: cover; display: block; }
.card-media.placeholder { background: linear-gradient(135deg, var(--gray-100), var(--gray-200)); }

/* Modules */
.module-list { list-style: none; margin: 0; padding: 0; border: 1px solid var(--border); border-radius: 8px; overflow: hidden; }
.module-item { display: grid; grid-template-columns: auto 1fr auto; gap: var(--sp-md); align-items: center; padding: var(--sp-lg); border-bottom: 1px solid var(--border); }
.module-item:last-child { border-bottom: 0; }
.module-number { display: inline-grid; place-items: center; width: 2rem; height: 2rem; background: var(--gray-100); color: var(--color-text-muted); border-radius: 999px; font-size: var(--fs-sm); }
.module-title { font-weight: var(--fw-medium); }
.module-duration { font-size: var(--fs-sm); color: var(--color-text-muted); justify-self: end; }

/* Guestbook */
.guest-form { display: grid; grid-template-columns: 1fr auto; gap: var(--sp-md); margin-bottom: var(--sp-lg); }
.input { padding: 0.75rem 0.875rem; border: 1px solid var(--border); border-radius: 8px; background: transparent; color: var(--color-text); }
.input:focus { outline: 2px solid var(--accent-blue); outline-offset: 2px; }
.button { padding: 0.7rem 1rem; border: 1px solid var(--border); background: var(--gray-100); color: var(--color-text); border-radius: 8px; cursor: pointer; }
[data-theme="dark"] .button { background: var(--gray-200); }
.guest-list { list-style: none; margin: 0; padding: 0; display: grid; gap: var(--sp-md); }
.guest-item { padding: var(--sp-md); border: 1px solid var(--border); border-radius: 8px; font-size: var(--fs-sm); color: var(--color-text-secondary); }

/* Footer */
.site-footer { border-top: 1px solid var(--border); padding: var(--sp-xl) 0; }
.footer-inner { display: flex; justify-content: center; color: var(--color-text-muted); font-size: var(--fs-sm); }

/* Accessibility helpers */
.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;
}

/* Responsive */
@media (max-width: 720px) {
  .nav { justify-content: flex-start; }
  .icon-button { margin-left: 0; }
  .hero { grid-template-columns: 1fr; }
  .hero-avatar { justify-self: start; }
}