body {
    font-family: Arial, sans-serif;
    margin: 0;
    padding: 0;
    background-color: #f4f4f9;
}
header {
    background-color: #333;
    color: #fff;
    padding: 10px 20px;
    text-align: center;
}
nav {
    display: flex;
    justify-content: center;
    background-color: #444;
}
nav a {
    color: #fff;
    padding: 10px 20px;
    text-decoration: none;
}
nav a:hover {
    background-color: #555;
}
.container {
    padding: 20px;
    max-width: 800px;
    margin: 0 auto;
}
.hidden {
    display: none;
}
form {
    margin-bottom: 20px;
}
input, select, button {
    display: block;
    margin: 10px 0;
    padding: 10px;
    width: 100%;
}
table {
    width: 100%;
    border-collapse: collapse;
    margin: 20px 0;
}
th, td {
    padding: 10px;
    border: 1px solid #ddd;
    text-align: left;
}
th {
    background-color: #333;
    color: #fff;
}
.btn {
    cursor: pointer;
    background-color: #333;
    color: #fff;
    border: none;
}
.btn:hover {
    background-color: #555;
}