html,
body {
  height: 100%;
  background-color: #f2f2f2;
}

header {
  background-color: #333;
  color: white;
  padding: 10px;
}

nav ul {
  list-style-type: none;
  margin: 0;
  padding: 0;
  display: flex;
}

nav li {
  margin-right: 20px;
}

nav li:last-child {
  margin-right: 0;
}

nav a {
  color: white;
  text-decoration: none;
}

#add-class-diagram-btn {
  background-color: #4CAF50;
  color: white;
  padding: 10px 20px;
  border: none;
  border-radius: 4px;
  cursor: pointer;
}

#add-object-diagram-btn {
  background-color: #4CAF50;
  color: white;
  padding: 10px 20px;
  border: none;
  border-radius: 4px;
  cursor: pointer;
}

#content {
  padding: 20px;
  background-color: #f2f2f2;
  height: 100%;
}

.hidden {
  display: none;
}

footer {
  position: absolute;
  bottom: 60px;
  right: 10px;
  font-size: 12px;
  color: gray;
}