body {
    margin: 0;
    font-family: Arial, sans-serif;
    background: #f5f5f5;
    color: #222;
    transition: background 0.3s ease, color 0.3s ease;
}
.dark {
    background: #1c1c1c;
    color: #e5e5e5;
}
header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 20px;
    background: #0077ff;
    color: white;
}
nav {
    display: flex;
    gap: 20px;
    padding: 20px;
}
.btn {
    text-decoration: none;
    background: #0077ff;
    color: white;
    padding: 12px 20px;
    border-radius: 8px;
    transition: 0.2s;
}
.btn:hover {
    background: #005fcc;
}