Generated by SassMeister.com.

SassMeister-input-HTML.html

<div class='container'>
  <div ='top'>
    <div class='ed'>
      foo
    </div>
    <div class='ed'>
      foo
    </div>
  </div>
  <div class='render'>
    bar
  </div>
</div>

SassMeister-input.scss

// ----
// Sass (v3.3.14)
// Compass (v1.0.1)
// Susy (v2.1.3)
// ----

@import "compass/reset";
@import "susy";
.container { 
  @include container(80em); 
  background-color : green;
}

.ed { 
  @include gallery(4 of 12);
  background-color: red;
  &:nth-child(1):nth-last-child(2),
  &:nth-child(2):nth-last-child(1) {
	  @include gallery(6 of 12);
  }
}
.render {
  @include full;
  background-color: yellow;
}

SassMeister-output.css

html, body, div, span, applet, object, iframe,
h1, h2, h3, h4, h5, h6, p, blockquote, pre,
a, abbr, acronym, address, big, cite, code,
del, dfn, em, img, ins, kbd, q, s, samp,
small, strike, strong, sub, sup, tt, var,
b, u, i, center,
dl, dt, dd, ol, ul, li,
fieldset, form, label, legend,
table, caption, tbody, tfoot, thead, tr, th, td,
article, aside, canvas, details, embed,
figure, figcaption, footer, header, hgroup,
menu, nav, output, ruby, section, summary,
time, mark, audio, video {
  margin: 0;
  padding: 0;
  border: 0;
  font: inherit;
  font-size: 100%;
  vertical-align: baseline;
}

html {
  line-height: 1;
}

ol, ul {
  list-style: none;
}

table {
  border-collapse: collapse;
  border-spacing: 0;
}

caption, th, td {
  text-align: left;
  font-weight: normal;
  vertical-align: middle;
}

q, blockquote {
  quotes: none;
}
q:before, q:after, blockquote:before, blockquote:after {
  content: "";
  content: none;
}

a img {
  border: none;
}

article, aside, details, figcaption, figure, footer, header, hgroup, main, menu, nav, section, summary {
  display: block;
}

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

.ed {
  width: 32.20339%;
  float: left;
  background-color: red;
}
.ed:nth-child(3n + 1) {
  margin-left: 0;
  margin-right: -100%;
  clear: both;
  margin-left: 0;
}
.ed:nth-child(3n + 2) {
  margin-left: 33.89831%;
  margin-right: -100%;
  clear: none;
}
.ed:nth-child(3n + 3) {
  margin-left: 67.79661%;
  margin-right: -100%;
  clear: none;
}
.ed:nth-child(1):nth-last-child(2), .ed:nth-child(2):nth-last-child(1) {
  width: 49.15254%;
  float: left;
}
.ed:nth-child(1):nth-last-child(2):nth-child(2n + 1), .ed:nth-child(2):nth-last-child(1):nth-child(2n + 1) {
  margin-left: 0;
  margin-right: -100%;
  clear: both;
  margin-left: 0;
}
.ed:nth-child(1):nth-last-child(2):nth-child(2n + 2), .ed:nth-child(2):nth-last-child(1):nth-child(2n + 2) {
  margin-left: 50.84746%;
  margin-right: -100%;
  clear: none;
}

.render {
  clear: both;
  width: 100%;
  float: left;
  margin-left: 0;
  margin-right: 0;
  background-color: yellow;
}

SassMeister-rendered.html

<div class='container'>
  <div ='top'>
    <div class='ed'>
      foo
    </div>
    <div class='ed'>
      foo
    </div>
  </div>
  <div class='render'>
    bar
  </div>
</div>