body {
  font-family: Arial, sans-serif;
  background-color: #f4f4f4;
  margin: 0;
  padding: 0;
}

.container {
  max-width: 800px;
  margin: 50px auto;
  background: #fff;
  padding: 20px;
  border-radius: 8px;
  box-shadow: 0 0 10px rgba(0, 0, 0, 0.1);
}

.hidden {
  display: none;
}

.error {
  color: red;
}

#nav-tabs {
  margin-top: 20px;
}

.tab-btn {
  padding: 10px 20px;
  cursor: pointer;
  background: #ddd;
  border: none;
  margin-right: 5px;
  border-radius: 4px;
}

.tab-btn.active {
  background: #aaa;
  color: #fff;
}

.tab-content {
  margin-top: 20px;
}

#header {
  display: flex;
  justify-content: space-between;
  align-items: center;
}

button {
  padding: 8px 16px;
  cursor: pointer;
  border: none;
  border-radius: 4px;
  background-color: #333;
  color: #fff;
}

button.hidden {
  display: none;
}

table {
  width: 100%;
  border-collapse: collapse;
}

table, th, td {
  border: 1px solid #ddd;
}

th, td {
  padding: 8px;
  text-align: left;
}