:root {
  --bg: #ffffff;
  --text: #111111;
  --muted: #555555;
  --border: #dddddd;
  --card: #f6f6f6;
}

body.dark {
  --bg: #0f0f12;
  --text: #f2f2f2;
  --muted: #c9c9c9;
  --border: #2a2a33;
  --card: #17171c;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: system-ui, -apple-system, Segoe UI, Roboto, Arial, sans-serif;
  background: var(--bg);
  color: var(--text);
}

.site-header {
  display: flex; /* ✅ flex requirement */
  align-items: center;
  gap: 16px;
  padding: 14px 18px;
  border-bottom: 1px solid var(--border);
}

.site-title {
  margin: 0;
  font-size: 1.1rem;
}

.main-nav {
  display: flex;
  gap: 10px;
  margin-left: auto;
}

.main-nav a {
  color: var(--text);
  text-decoration: none;
  padding: 8px 10px;
  border-radius: 10px;
  border: 1px solid transparent;
}

.main-nav a:hover {
  background: var(--card);
  border-color: var(--border);
}

.theme-button {
  padding: 8px 10px;
  border-radius: 10px;
  border: 1px solid var(--border);
  background: var(--card);
  color: var(--text);
  cursor: pointer;
}

.main-content {
  max-width: 900px;
  margin: 0 auto;
  padding: 18px;
}

.hero {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 16px;
}

.hero h2 {
  margin: 0 0 8px 0;
}

.hero p {
  margin: 0;
  color: var(--muted);
  line-height: 1.5;
}

@media (max-width: 640px) {
  .site-header {
    flex-wrap: wrap;
  }

  .main-nav {
    width: 100%;
    margin-left: 0;
  }
}