body {
    font-family: sans-serif;
    margin: 20px;
}
.container {
    max-width: 800px;
    margin: 0 auto;
}
h1, h2 {
    text-align: center;
}
nav ul {
    list-style: none;
    padding: 0;
    text-align: center;
    margin-bottom: 20px;
}
nav ul li {
    display: inline;
    margin: 0 10px;
}
nav a {
    text-decoration: none;
    color: #007bff;
}
.form-group {
    margin-bottom: 10px;
}
label {
    display: block;
    margin-bottom: 5px;
    font-weight: bold;
}
input[type="text"], input[type="number"], select {
    width: calc(100% - 12px);
    padding: 8px;
    border: 1px solid #ddd;
    border-radius: 3px;
    box-sizing: border-box;
}
button {
    padding: 10px 15px;
    background-color: #007bff;
    color: white;
    border: none;
    border-radius: 5px;
    cursor: pointer;
}
button:hover {
    background-color: #0056b3;
}
table {
    width: 100%;
    border-collapse: collapse;
    margin-top: 10px;
}
th, td {
    border: 1px solid #ccc;
    padding: 8px;
    text-align: left;
}
th {
    background-color: #f2f2f2;
}
.total {
    font-weight: bold;
    text-align: right;
    padding-top: 10px;
}
#invoice-preview {
    margin-top: 30px;
    border: 1px solid #aaa;
    padding: 20px;
    border-radius: 5px;
}
#invoice-preview h2 {
    margin-top: 0;
}
.actions {
    margin-top: 20px;
    text-align: center;
}
.actions button {
    margin: 0 10px;
}
.product-selection, .buyer-selection {
    margin-bottom: 20px;
    padding: 15px;
    border: 1px solid #ccc;
    border-radius: 5px;
}
.product-list, .buyer-list, .add-product-form, .add-buyer-form {
    margin-bottom: 20px;
    padding: 15px;
    border: 1px solid #ccc;
    border-radius: 5px;
}
.product-list button, .buyer-list button {
    margin-left: 5px;
    background-color: #dc3545;
}
.product-list button:hover, .buyer-list button:hover {
    background-color: #c82333;
}