body {
    font-family: Arial, sans-serif;
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    background-color: #f4f4f4;
}

header {
    background-color: #333;
    color: #fff;
    text-align: center;
    padding: 1em 1em 0 1em;
    border-bottom: 2px solid #ffff61;
}

header nav ul {
    list-style: none;
}

header nav ul li {
    display: inline;
    margin: 0 10px;
    padding: 1em 0.5em;
}

header nav ul .nav-item.active .nav-link{
    color: black;
    background-color: #F4F4F4;
    border-radius: 4px;
    padding: 1em 0.5em;
    border-bottom: 3px solid #F4F4F4;
    border-top: 2px solid #ffff61;
    border-left: 2px solid #ffff61;
    border-right: 2px solid #ffff61;

}

header nav ul li a {
    color: #fff;
    text-decoration: none;
    font-weight: bold;
}
header nav ul li a:hover {
    color: #ffff61;
}

main {
    max-width: 800px;
    margin: 20px auto;
    background-color: #fff;
    padding: 20px;
    box-shadow: 0 0 10px rgba(0, 0, 0, 0.1);
}

footer {
    background-color: #333;
    color: #fff;
    text-align: center;
    padding: 10px 0;
    position: fixed;
    width: 100%;
    bottom: 0;
}