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

header {
    background: #333;
    padding: 10px;
}

header nav a {
    color: white;
    text-decoration: none;
    margin-right: 15px;
}

header nav a:hover {
    text-decoration: underline;
}

h1 {
    text-align: center;
    margin-top: 20px;
}

.category-list, .notes-list, .cart-list {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
}

.category-card, .note-card, .cart-item {
    border: 1px solid #ddd;
    padding: 15px;
    margin: 10px;
    width: 250px;
    text-align: center;
}

.note-card img, .cart-item img{
    max-width: 100%;
}

.category-card img {
    height: 20vh;
}

.btn {
    display: inline-block;
    padding: 8px 15px;
    background: green;
    color: white;
    text-decoration: none;
    border-radius: 4px;
    margin-top: 10px;
}

.btn:hover {
    background: darkgreen;
}

.remove-btn {
    background: red;
}

.remove-btn:hover {
    background: darkred;
}

.pay-btn {
    background: blue;
}

footer {
    text-align: center;
    padding: 15px;
    background: #333;
    color: white;
    margin-top: 20px;
}

.messages {
    list-style-type: none;
    padding: 0;
    text-align: center;
}

.messages li {
    padding: 10px;
    margin: 10px;
    border-radius: 4px;
}

.messages .success {
    background: lightgreen;
}

.messages .error {
    background: pink;
}

.messages .warning {
    background: lightyellow;
}