body{
  background: skyblue;
}

.wrapper{
  width: 960px;
  margin: auto;
}

main{
  float: left;
  width: 640px;
}

main ol{
  list-style-type: decimal-leading-zero;
}

aside{
  float: right;
  width: 320px;
}

a:hover{
  color: red;
}

footer{
  clear: both;
}

.intro{
  background: white;
  border-radius: 5px;
  box-shadow: 10px 5px 5px navy;
}