body {
    margin: 0;
    font-family: Arial, Helvetica, sans-serif;
    background-color: #f4f6f9;
    height: 100vh;
    display: flex;
    flex-direction: column;
    transition: 0.3s ease;
}

.header {
    background-color: #2c3e50;
    color: white;
    padding: 20px;
    text-align: center;
}

.menu {
    background-color: #34495e;
    color: white;
    padding: 10px;
    text-align: center;
}

.main-container {
    flex: 1;
    display: flex;
    overflow: hidden;
}

.sidebar {
    width: 230px;
    background: linear-gradient(180deg, #ecf0f1, #d6e4f0);
    padding: 20px;
    overflow-y: auto;
    border-right: 3px solid #3498db;
}

.sidebar h3 {
    margin-top: 20px;
    margin-bottom: 10px;
    padding: 8px 10px;
    background-color: #3498db;
    color: white;
    border-radius: 6px;
    cursor: pointer;
    transition: 0.3s ease;
}

.sidebar h3:hover {
    background-color: #2980b9;
}

.sidebar button {
    width: 100%;
    margin-bottom: 10px;
    padding: 9px;
    border: none;
    background-color: white;
    color: #2c3e50;
    border-left: 4px solid #3498db;
    border-radius: 6px;
    cursor: pointer;
    font-size: 14px;
    transition: 0.3s ease;
}

.sidebar button:hover {
    background-color: #3498db;
    color: white;
}

.content {
    flex: 1;
    padding: 60px 40px;
    overflow-y: auto;
    display: flex;
    justify-content: center;
    align-items: flex-start;
}

.card {
    background-color: white;
    padding: 35px;
    width: 100%;
    max-width: 650px;
    border-radius: 14px;
    box-shadow: 0 12px 30px rgba(0, 0, 0, 0.08);
    animation: fadeIn 0.3s ease-in-out;
    transition: 0.3s ease;
}

.content h2 {
    margin-bottom: 25px;
    font-size: 28px;
    color: #2c3e50;
}

.content input {
    padding: 10px;
    margin: 8px;
    font-size: 16px;
    border-radius: 6px;
    border: 1px solid #ccc;
}

.content button {
    padding: 10px 16px;
    margin: 8px;
    font-size: 15px;
    border: none;
    border-radius: 6px;
    background-color: #3498db;
    color: white;
    cursor: pointer;
    transition: 0.3s ease;
}

.content button:hover {
    background-color: #2980b9;
}

body.dark-mode {
    background-color: #222;
    color: white;
}

body.dark-mode .card {
    background-color: #333;
    color: white;
}

.footer {
    background-color: #2c3e50;
    color: white;
    text-align: center;
    padding: 15px;
}

ul {
    padding-left: 20px;
    margin-top: 20px;
}

li {
    margin: 8px 0;
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(10px); }
    to { opacity: 1; transform: translateY(0); }
}