body {
  font: normal 90% "Trebuchet MS", Verdana, "Lucida Grande", Tahoma, Arial,
    Helvetica, Sans-Se- rif;
  color: #1b00b1;
  background: #cecccc;
  font-size: 140%;
  padding: 0 20px 2em;
  margin: 0 auto;
  max-width: 1000px;
  box-sizing: border-box;
}

header {
  width: 100%;
  height: 100px;
  background-color: #f0f0f0;
}

nav {
  width: 100%;
  height: 50px;
  background-color: #e0e0e0;
}

aside {
  width: 20%;
  height: 800px;
  float: left;
  background-color: #858484;
}

section {
  width: 80%;
  height: 800px;
  float: left;
  background-color: #d0d0d0;
}

article {
  width: 80%;
  margin: 0 auto;
  height: 600px;
  background-color: #c0c0c0;
}

footer {
  clear: both;
  width: 100%;
  height: 100px;
  background-color: #5e5e5e;
}

.content {
  width: 70%;
  float: left;
}

.image {
  width: 30%;
  float: right;
}

@media screen and (max-width: 640px) {
  aside,
  section {
    width: 100%;
    height: auto;
    float: none;
  }
  .content {
    color: yellow;
  }

  .image {
    width: 100%;
    float: none;
  }
}