* {
  box-sizing: border-box;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, sans-serif;
  line-height: 1.7;
  margin: 0;
  padding: 0;
  color: #1a1a1a;
  background: #fafafa;
}

.container {
  display: flex;
  min-height: 100vh;
}

/* Sidebar */
.sidebar {
  width: 260px;
  background: #f5f5f5;
  border-right: 1px solid #e0e0e0;
  padding: 1.5rem;
  position: fixed;
  height: 100vh;
  overflow-y: auto;
}

.sidebar h2 {
  font-size: 1.1rem;
  margin: 0 0 1rem 0;
  padding: 0;
  border: none;
}

.sidebar a {
  color: #1976d2;
  text-decoration: none;
}

.sidebar a:hover {
  text-decoration: underline;
}

.sidebar ul {
  list-style: none;
  padding: 0;
  margin: 0;
}

.sidebar li {
  margin: 0.4rem 0;
  font-size: 0.9rem;
}

.sidebar li.active a {
  font-weight: 600;
  color: #111;
}

.sidebar .section-label {
  font-weight: 600;
  color: #666;
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-top: 1.5rem;
  margin-bottom: 0.5rem;
}

/* Main content */
.content {
  margin-left: 260px;
  padding: 2rem 3rem;
  max-width: 800px;
  flex: 1;
}

h1 {
  font-size: 2rem;
  margin-bottom: 0.5rem;
  color: #111;
}

h2 {
  font-size: 1.5rem;
  margin-top: 2.5rem;
  padding-top: 1rem;
  border-top: 1px solid #e0e0e0;
  color: #222;
}

h3 {
  font-size: 1.2rem;
  margin-top: 2rem;
  color: #333;
}

p {
  margin: 1rem 0;
}

code {
  font-family: "SF Mono", Consolas, "Liberation Mono", Menlo, monospace;
  font-size: 0.9em;
  background: #f0f0f0;
  padding: 0.15em 0.4em;
  border-radius: 3px;
}

pre {
  background: #1e1e1e;
  color: #d4d4d4;
  padding: 1rem;
  border-radius: 6px;
  overflow-x: auto;
  font-size: 0.9rem;
  line-height: 1.5;
  position: relative;
}

.copy-button {
  position: absolute;
  top: 0.5rem;
  right: 0.5rem;
  background: #3a3a3a;
  border: 1px solid #555;
  color: #ccc;
  padding: 0.25rem 0.5rem;
  border-radius: 4px;
  font-size: 0.75rem;
  cursor: pointer;
  opacity: 0;
  transition: opacity 0.2s, background 0.2s;
}

pre:hover .copy-button {
  opacity: 1;
}

.copy-button:hover {
  background: #4a4a4a;
  color: #fff;
}

.copy-button.copied {
  background: #2e7d32;
  border-color: #4caf50;
  color: #fff;
}

pre code {
  background: none;
  padding: 0;
  color: inherit;
}

table {
  width: 100%;
  border-collapse: collapse;
  margin: 1.5rem 0;
  font-size: 0.95rem;
}

th, td {
  padding: 0.75rem;
  text-align: left;
  border-bottom: 1px solid #e0e0e0;
}

th {
  background: #f5f5f5;
  font-weight: 600;
}

.hint {
  background: #e8f4fd;
  border-left: 4px solid #2196f3;
  padding: 1rem;
  margin: 1.5rem 0;
}

.exercise {
  background: #fff8e1;
  border-left: 4px solid #ff9800;
  padding: 1rem;
  margin: 1.5rem 0;
}

.warning {
  background: #ffebee;
  border-left: 4px solid #f44336;
  padding: 1rem;
  margin: 1.5rem 0;
}

.revised {
  background: #e8f5e9;
  border-left: 4px solid #4caf50;
  padding: 0.75rem 1rem;
  margin: 1.5rem 0;
  font-size: 0.9rem;
}

a {
  color: #1976d2;
}

.nav {
  display: flex;
  justify-content: space-between;
  margin-top: 3rem;
  padding-top: 1rem;
  border-top: 1px solid #e0e0e0;
}

.nav a {
  color: #1976d2;
  text-decoration: none;
}

.nav a:hover {
  text-decoration: underline;
}

.attribution {
  margin-top: 3rem;
  padding-top: 1rem;
  border-top: 1px solid #e0e0e0;
  font-size: 0.85rem;
  color: #666;
}

/* Mobile */
@media (max-width: 768px) {
  .sidebar {
    position: relative;
    width: 100%;
    height: auto;
    border-right: none;
    border-bottom: 1px solid #e0e0e0;
  }
  .container {
    flex-direction: column;
  }
  .content {
    margin-left: 0;
    padding: 1.5rem;
  }
}