body {
  margin: 0;
  font-family: 'Segoe UI', 'Meiryo', sans-serif;
  background: #f4f4f4;
}

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

.sidebar {
  width: 220px;
  background: #2c3e50;
  color: #fff;
  padding: 30px 20px;
  box-sizing: border-box;
}

.sidebar h2 {
  margin-top: 0;
  font-size: 1.5em;
  margin-bottom: 1em;
}

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

.sidebar ul li {
  margin-bottom: 1em;
}

.sidebar ul li a {
  color: #fff;
  text-decoration: none;
  font-size: 1.1em;
  transition: color 0.2s;
}

.sidebar ul li a:hover {
  color: #1abc9c;
}

.content {
  flex: 1;
  padding: 40px;
  background: #fff;
  box-sizing: border-box;
}

@media (max-width: 700px) {
  .container {
    flex-direction: column;
  }
  .sidebar {
    width: 100%;
    padding: 15px 10px;
  }
  .content {
    padding: 20px;
  }
}

.collapsible-header {
  cursor: pointer;
  display: block;
  padding: 0.5em 0;
  font-size: 1.1em;
  color: #fff;
  user-select: none;
}

.collapsible-content {
  padding-left: 1em;
  background: #34495e;
  border-radius: 4px;
  margin-top: 0.5em;
  margin-bottom: 0.5em;
}

.collapsible-content li {
  margin-bottom: 0.5em;
}

.collapsible-content li a {
  color: #ecf0f1;
  font-size: 1em;
}

.collapsible-content li a:hover {
  color: #1abc9c;
}