Generated by SassMeister.com.

SassMeister-input-HTML.html

<article>
  <ul>
    <li></li>
    <li></li>
    <li></li>
    <li></li>
  </ul>
</article>

SassMeister-input.scss

// ----
// Sass (v3.4.12)
// Compass (v1.0.3)
// Bourbon (v4.2.0)
// Neat (v1.6.0)
// ----

@import "bourbon/bourbon";
@import "neat/neat";

$s-viewport: new-breakpoint(max-width 480px);

article {
  @include outer-container;
  background-color: blue;
}
ul {
  margin: 0;
  padding: 0;
  li {
    list-style: none;
    min-height: 100px;
    background: red;
    margin-top: 10px;
    margin-bottom: 10px;
    @include media($s-viewport) {
      @include span-columns(6);
      &:nth-of-type(2n){
        @include omega;
      }
    }
  }
}

SassMeister-output.css

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

article {
  *zoom: 1;
  max-width: 68em;
  margin-left: auto;
  margin-right: auto;
  background-color: blue;
}
article:before, article:after {
  content: " ";
  display: table;
}
article:after {
  clear: both;
}

ul {
  margin: 0;
  padding: 0;
}
ul li {
  list-style: none;
  min-height: 100px;
  background: red;
  margin-top: 10px;
  margin-bottom: 10px;
}
@media screen and (max-width: 480px) {
  ul li {
    float: left;
    display: block;
    margin-right: 2.35765%;
    width: 48.82117%;
  }
  ul li:last-child {
    margin-right: 0;
  }
  ul li:nth-of-type(2n) {
    margin-right: 0;
  }
}

SassMeister-rendered.html

<article>
  <ul>
    <li></li>
    <li></li>
    <li></li>
    <li></li>
  </ul>
</article>