Generated by SassMeister.com.

SassMeister-input-HTML.html

<div class="container">
  <main>Main</main>
  <aside>Aside</aside>
  <footer>Footer</footer>
</div>

SassMeister-input.scss

// ----
// Sass (v3.3.7)
// Compass (v1.0.0.alpha.18)
// Breakpoint (v2.4.2)
// Susy (v2.1.2)
// ----

@import "susy";
@import "breakpoint";

.container {
  @include container(80%);
}

$susy: (
  columns: 12,
  gutters: 1/2,
);

@include breakpoint(40em) {
  
}

main {
  background-color: orange;
  @include span(9);
}

aside {
  background-color: dodgerblue;
  @include span(3 last);
}

footer {
  background-color: yellow;
  clear: left;
  @include span(4 at 2);
}

SassMeister-output.css

.container {
  max-width: 80%;
  margin-left: auto;
  margin-right: auto;
}
.container:after {
  content: " ";
  display: block;
  clear: both;
}

main {
  background-color: orange;
  width: 74.28571%;
  float: left;
  margin-right: 2.85714%;
}

aside {
  background-color: dodgerblue;
  width: 22.85714%;
  float: right;
  margin-right: 0;
}

footer {
  background-color: yellow;
  clear: left;
  width: 31.42857%;
  float: left;
  margin-right: 2.85714%;
}

SassMeister-rendered.html

<div class="container">
  <main>Main</main>
  <aside>Aside</aside>
  <footer>Footer</footer>
</div>