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

body {
  font-family: Arial, sans-serif;
  background: #ffffff;
  color: #222;
  line-height: 1.6;
}

header {
  background: #f4f4f4;
  padding: 20px;
  text-align: center;
}

header h1 {
  font-size: 2em;
  margin-bottom: 5px;
}

header nav a {
  text-decoration: none;
  color: #28a745;
  font-weight: bold;
  margin-right: 15px;
}

.container {
  display: flex;
  max-width: 1200px;
  margin: 20px auto;
  flex-wrap: wrap;
}

aside {
  flex: 1 1 250px;
  background: #e2e2e2;
  padding: 20px;
  border-radius: 6px;
  margin-right: 20px;
}

aside h2 {
  margin-bottom: 10px;
}

aside ul {
  list-style: none;
  padding: 0;
}

aside ul li {
  margin-bottom: 10px;
}

aside ul li a {
  text-decoration: none;
  color: #222;
  font-weight: bold;
  padding: 6px 10px;
  display: block;
  border-radius: 4px;
  transition: background 0.2s;
}

aside ul li a:hover {
  background: #d1d1d1;
}

main {
  flex: 3 1 700px;
  padding: 20px;
  min-width: 300px;
}

main h2 {
  margin-bottom: 10px;
}

main p {
  margin-bottom: 15px;
}

pre {
  background: #f4f4f4;
  padding: 10px;
  overflow-x: auto;
  border-left: 4px solid #333;
  margin-bottom: 15px;
}

footer {
  text-align: center;
  padding: 15px;
  background: #f4f4f4;
  margin-top: 20px;
  border-top: 1px solid #ccc;
}

/* Next Lesson Button */
.next-lesson {
  margin-top: 40px;
  text-align: right;
}

.next-lesson a {
  display: inline-block;
  background-color: #28a745;
  color: white;
  text-decoration: none;
  padding: 12px 20px;
  border-radius: 8px;
  font-weight: bold;
  transition: background 0.3s;
}

.next-lesson a:hover {
  background-color: #218838;
}

.next-lesson .arrow {
  margin-left: 10px;
  font-weight: bold;
}

/* Responsive adjustments */
@media (max-width: 768px) {
  .container {
    flex-direction: column;
  }

  aside {
    margin-right: 0;
    margin-bottom: 20px;
  }
}

/* Dark Mode Example */
body.dark-mode {
  background: #1e1e1e;
  color: #f4f4f4;
}

body.dark-mode header,
body.dark-mode footer {
  background: #333;
  color: #f4f4f4;
}

body.dark-mode aside {
  background: #2c2c2c;
}