body {
    font-family: Arial, sans-serif;
    margin: 0;
    padding: 0;
}
header, footer {
    background-color: #333;
    color: white;
    padding: 1em;
    text-align: center;
}
nav a {
    color: white;
    margin: 0 15px;
    text-decoration: none;
}
main {
    padding: 20px;
}
.responsive-img {
    max-width: 100%;
    height: auto;
}