body {
  font-family: Arial, sans-serif;
  margin: 0; padding: 0;
  background: #f5f5f5;
}

header {
  background: #4CAF50;
  color: white;
  padding: 1rem;
  text-align: center;
}

#auth-section, #main-content {
  margin: 2rem auto;
  max-width: 600px;
  background: white;
  padding: 1.5rem;
  border-radius: 10px;
  box-shadow: 0px 2px 6px rgba(0,0,0,0.1);
}

button {
  background: #4CAF50;
  color: white;
  border: none;
  padding: 0.6rem 1rem;
  cursor: pointer;
  border-radius: 5px;
}

button:hover {
  background: #45a049;
}

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

li {
  padding: 0.7rem;
  margin: 0.5rem 0;
  background: #e3f2fd;
  cursor: pointer;
  border-radius: 5px;
  transition: 0.3s;
}

li:hover {
  background: #bbdefb;
}

.hidden {
  display: none;
}

.completed {
  text-decoration: line-through;
  color: gray;
}