CSS 代码 

/* styles.css */
body {
font-family: Arial, sans-serif;
margin: 0;
padding: 0;
}

header {
background-color: #333;
color: #fff;
padding: 1em;
text-align: center;
}

nav {
background-color: #444;
}

nav ul {
list-style: none;
padding: 0;
margin: 0;
display: flex;
justify-content: center;
}

nav ul li {
margin: 0 1em;
}

nav ul li a {
color: #fff;
text-decoration: none;
}

main {
padding: 2em;
text-align: center;
}

footer {
background-color: #333;
color: #fff;
padding: 1em;
text-align: center;
}

.container {
display: flex;
flex-wrap: wrap;
gap: 10px;
}

.item {
flex: 1 1 30%;
background-color: #f4f4f4;
padding: 1em;
}

.grid-container {
display: grid;
grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
gap: 10px;
}

.grid-item {
background-color: #f4f4f4;
padding: 1em;
}

@media (max-width: 768px) {
body {
font-size: 14px;
}

nav ul {
flex-direction: column;
}
}

@media (max-width: 480px) {
body {
font-size: 12px;
}
}