:root {
  --bg-color: #f8f9fa;
  --text-color: #212529;
  --sidebar-bg: #e9ecef;
  --sidebar-text: #343a40;
  --accent-color: #0056b3;
  --border-color: #dee2e6;
  --hover-bg: #ced4da;
  --transition-speed: 0.3s;
}

[data-theme="dark"] {
  --bg-color: #121212;
  --text-color: #e0e0e0;
  --sidebar-bg: #1e1e1e;
  --sidebar-text: #f8f9fa;
  --accent-color: #4da3ff;
  --border-color: #333;
  --hover-bg: #2c2c2c;
}

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

body {
  font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
  background: var(--bg-color);
  color: var(--text-color);
  line-height: 1.6;
  transition: background var(--transition-speed), color var(--transition-speed);
}

header {
  display: grid;
  grid-template-columns: auto 1fr auto;
  align-items: center;
  gap: 1rem;
  padding: 0.8rem 2rem;
  background: var(--sidebar-bg);
  border-bottom: 1px solid var(--border-color);
  position: sticky;
  top: 0;
  z-index: 100;
}

.brand {
  display: flex;
  align-items: center;
  text-decoration: none;
}

.logo-svg {
  height: 32px;
  width: auto;
  transition: transform 0.2s ease;
}

.brand:hover .logo-svg {
  transform: scale(1.03);
}

.header-title {
  text-align: center;
}

.site-name {
  font-size: 1.2rem;
  font-weight: 600;
  color: var(--text-color);
  margin: 0;
  white-space: nowrap;
}

#theme-toggle {
  padding: 0.5rem 1rem;
  background: var(--accent-color);
  color: white;
  border: none;
  border-radius: 6px;
  cursor: pointer;
  font-size: 0.9rem;
  transition: opacity var(--transition-speed);
}

#theme-toggle:hover {
  opacity: 0.85;
}

.container {
  display: flex;
  min-height: calc(100vh - 60px);
}

.sidebar {
  width: 260px;
  background: var(--sidebar-bg);
  padding: 1.5rem;
  border-right: 1px solid var(--border-color);
  position: sticky;
  top: 60px;
  height: calc(100vh - 60px);
  overflow-y: auto;
  flex-shrink: 0;
}

.sidebar ul {
  list-style: none;
}

.sidebar a {
  display: block;
  padding: 0.6rem 0.8rem;
  color: var(--sidebar-text);
  text-decoration: none;
  border-radius: 6px;
  margin-bottom: 0.3rem;
  transition: background var(--transition-speed), color var(--transition-speed);
}

.sidebar a:hover,
.sidebar a:focus {
  background: var(--hover-bg);
  color: var(--accent-color);
  outline: none;
}

main {
  flex: 1;
  padding: 2rem;
  max-width: 900px;
}

section {
  margin-bottom: 3rem;
  scroll-margin-top: 80px;
}

h2 {
  margin-bottom: 1rem;
  color: var(--accent-color);
  font-weight: 600;
}

p, li {
  margin-bottom: 0.8rem;
}

ul {
  padding-left: 1.5rem;
}

a {
  color: var(--accent-color);
  text-decoration: none;
}

a:hover {
  text-decoration: underline;
}

footer {
  margin-top: 3rem;
  padding: 2rem;
  border-top: 1px solid var(--border-color);
  text-align: center;
  font-size: 0.9rem;
  color: var(--text-color);
}

footer nav {
  margin-top: 0.5rem;
}

footer nav a {
  margin: 0 0.5rem;
  color: var(--accent-color);
  font-weight: 500;
}

@media (max-width: 768px) {
  .container {
    flex-direction: column;
  }
  .sidebar {
    width: 100%;
    height: auto;
    position: relative;
    top: 0;
    border-right: none;
    border-bottom: 1px solid var(--border-color);
    padding: 1rem;
  }
  main {
    padding: 1.5rem;
  }
  header {
    grid-template-columns: auto 1fr auto;
    gap: 0.5rem;
    padding: 0.8rem 1rem;
  }
  .site-name {
    font-size: 0.95rem;
  }
  .logo-svg {
    height: 28px;
  }
  footer {
    padding: 1.5rem 1rem;
  }
}