body {
  font-family: Arial, sans-serif;
  background: #f4f6f8;
  margin: 0;
  padding: 0;
  color: #333;
}
nav {
  background: #0f172a;
  padding: 12px 20px;
}

nav ul {
  list-style: none;
  display: flex;
  gap: 20px;
  margin: 0;
  padding: 0;
  align-items: center;
}

nav ul li a {
  color: #e5e7eb;
  text-decoration: none;
  font-size: 15px;
  font-weight: 500;
  padding: 8px 12px;
  border-radius: 6px;
  transition: background 0.3s ease, color 0.3s ease;
}

nav ul li a:hover {
  background: #4f46e5;
  color: #fff;
}
@media (max-width: 400px) {
  nav ul {
    flex-direction: column;
    gap: 2px;
  }
}

.site-header {
  background: #0073aa;
  color: white;
  padding: 20px;
  text-align: center;
}
p {
  font-size: 17px;
  line-height: 1.9;
  color: #444;
  background: #f9f9f9;
  padding: 15px 18px;
  border-left: 4px solid #0073aa;
  border-radius: 6px;
  margin: 20px 0;
}

.lesson-container {
  max-width: 900px;
  margin: 30px auto;
  padding: 15px;
}

.lesson-box {
  background: white;
  padding: 20px;
  margin-bottom: 20px;
  border-left: 5px solid #0073aa;
  box-shadow: 0 2px 6px rgba(0,0,0,0.1);
}

.lesson-box h2,
.lesson-box h3 {
  margin-top: 0;
}

pre {
  background: #1e1e1e;
  color: white;
  padding: 15px;
  overflow-x: auto;
  border-radius: 6px;
}

.lesson-nav {
  display: flex;
  justify-content: space-between;
}

.btn {
  text-decoration: none;
  background: #0073aa;
  color: white;
  padding: 10px 18px;
  border-radius: 4px;
}

.btn.disabled {
  background: #ccc;
  pointer-events: none;
}
footer {
  background: #111827;
  padding: 20px 10px;
  text-align: center;
  margin-top: 40px;
}

footer a {
  color: #d1d5db;
  text-decoration: none;
  margin: 0 10px;
  font-size: 14px;
  transition: color 0.3s ease;
}

footer a:hover {
  color: #4f46e5;
}

footer a:focus {
  outline: none;
}

.site-footer {
  text-align: center;
  padding: 15px;
  background: #222;
  color: #ccc;
}