body {
  font-family: Arial, sans-serif;
  margin: 0;
  padding: 0;
}

header, nav, aside, footer {
  background-color: #f0f8ff;
  padding: 10px;
  text-align: center;
}

nav a {
  margin: 0 15px;
  text-decoration: none;
  color: #333;
}

main {
  padding: 20px;
}

img, video, audio {
  max-width: 100%;
  height: auto;
}

@media (max-width: 768px) {
  nav, aside {
    display: block;
    text-align: center;
  }
}