body {
    font-family: Arial, sans-serif;
    line-height: 1.6;
    margin: 0;
    padding: 20px;
    background-color: #f4f4f4;
}
.container {
    max-width: 1000px;
    margin: auto;
    background: white;
    padding: 20px;
    box-shadow: 0 0 10px rgba(0,0,0,0.1);
}
nav {
    background: #333;
    color: #fff;
    padding: 10px;
    margin-bottom: 20px;
}
nav a {
    color: #fff;
    text-decoration: none;
    padding: 5px 10px;
}
h1, h2, h3, h4 {
    color: #333;
}
form {
    margin-bottom: 20px;
}
input, select, textarea {
    width: 100%;
    padding: 8px;
    margin-bottom: 10px;
}
button {
    background: #333;
    color: #fff;
    padding: 10px 15px;
    border: none;
    cursor: pointer;
}
button:hover {
    background: #555;
}
#customerList {
    margin-top: 20px;
}
.customer-item {
    background: #f4f4f4;
    padding: 10px;
    margin-bottom: 20px;
    border: 1px solid #ddd;
    border-radius: 5px;
}
.warranty-checkbox {
    display: inline-block;
    margin-right: 10px;
}
.modal {
    display: none;
    position: fixed;
    z-index: 1;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    overflow: auto;
    background-color: rgba(0,0,0,0.4);
}
.modal-content {
    background-color: #fefefe;
    margin: 15% auto;
    padding: 20px;
    border: 1px solid #888;
    width: 80%;
    max-width: 500px;
}
.close {
    color: #aaa;
    float: right;
    font-size: 28px;
    font-weight: bold;
}
.close:hover,
.close:focus {
    color: black;
    text-decoration: none;
    cursor: pointer;
}
.invoice-list {
    margin-left: 20px;
    border-left: 2px solid #ccc;
    padding-left: 10px;
}
.create-invoice-btn {
    background-color: #4CAF50;
    color: white;
    padding: 10px 15px;
    border: none;
    cursor: pointer;
    margin-top: 10px;
}
.create-invoice-btn:hover {
    background-color: #45a049;
}
.invoice-group {
    margin-bottom: 20px;
    padding: 10px;
    background-color: #f9f9f9;
    border: 1px solid #ddd;
    border-radius: 5px;
}
.invoice-group h3 {
    margin-top: 0;
}
.invoice-item {
    margin-bottom: 10px;
    padding: 5px;
    border: 1px solid #ddd;
    border-radius: 3px;
    background-color: #fff;
}
.status-select {
    padding: 5px;
    margin-left: 10px;
}