Layout markup standard

HTML

<header></header>
<div class="content">
  <aside class="pre"></aside>
  <article></article>
  <aside class="post"></aside>
</div>
<footer></footer>

CSS

header {
    width: 100%;
    height: 30px;
    background-color: red;
    margin: 0 auto;
}
.content {
    max-width: 250px;
    margin: 0 auto;
    background-color: yellow;
    overflow: hidden;
}
aside, article {
    float: left;
    height: 250px;
}
aside {
    width: 50px;
    background-color: magenta
}
article {
    width: 150px;
    background-color: blue;
}
footer {
    width: 100%;
    height: 10px;
    margin: 0 auto;
    background-color: orange;
}