* {
  -webkit-box-sizing: border-box;
  -moz-box-sizing: border-box;
  box-sizing: border-box;
}

main {
  max-width: 68em;
  margin-left: auto;
  margin-right: auto;
}
main:after {
  content: "";
  display: table;
  clear: both;
}

article {
  float: left;
  display: block;
  margin-right: 2.35765%;
  width: 82.94039%;
  background-color: red;
}
article:last-child {
  margin-right: 0;
}
@media screen and (max-width: 900px) {
  article {
    float: right;
  }
}

aside {
  float: left;
  display: block;
  margin-right: 2.35765%;
  width: 14.70196%;
  background-color: blue;
}
aside:last-child {
  margin-right: 0;
}
@media screen and (max-width: 900px) {
  aside {
    float: left;
  }
}