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

nav {
  background: black;
  padding: 10px;
  text-align: center;
}

nav div {
  display: inline-block;
  background: darkblue;
  color: white;
  padding: 8px 12px;
  margin: 4px;
}

.layout2 div {
  height: 100px;
  margin: 10px;
}

.header {
  background: pink;
}

.sidebar {
  background: lightgreen;
}

.main {
  background: lightyellow;
}

.footer {
  background: lightgray;
}

@media (min-width: 800px) {
  .layout2 {
    display: flex;
    flex-wrap: wrap;
  }

  .sidebar {
    width: 30%;
  }

  .main {
    width: 68%;
    margin-left: 2%;
  }

  .header, .footer {
    width: 100%;
  }
}