Generated by SassMeister.com.

SassMeister-input-HTML.haml

.wrap
  .content
    %h2 Content
    .gallery
      -3.times do | i| 
        .gallery__item.level-1
          %h2 Item #{i+1}
          - if i < 2
            - 2.times do | x |
              .gallery__subitem.level-2
                - if i > 0
                  %h2 SubItem #{x+1}
                -else
                  %h2 SubItem #{x+3}
      .full
        %h2 Full Wide Item
  .sidebar
    %h2
      Sidebar

SassMeister-input.scss

// ----
// libsass (v3.2.5)
// ----

// Nested: Second edition after review feedback from me & others; practice makes perfect
@import "susy";
@import "toolkit";
@import "toolkit/kickstart";
@import "breakpoint";

//Variables
$breakpoint-to-ems: true;
$susy: ( columns: 8, debug: (image: show, color: rgba(#66f, .25)), global-box-sizing: border-box, container: 1140px, gutter-position: after);
$tablet: 600px;
$desktop: 980px;

// Mixins
@mixin cf {
  &:after {
    content: " ";
    display: block;
    clear: both;
  }
}


:root {
  font-family: sans-serif;
}
ul, ol, li {
  margin: 0;
  padding: 0;
}

li {
  list-style: none;
}

.wrap {
  @include container();
  padding: {
  };
  
}

.content {
  margin-top: 10vh;
  background: rgba(113, 218, 210, 0.8);
  @include span(6);
}

.sidebar {
  margin-top: 10vh;
  background: rgba(250, 231, 179, 0.8);
  @include span(2 last);
  
  a {
    color: #666;
    padding-left: 1rem;
    line-height: 2;
    text-decoration: none;
  }
}


h2 { 
  padding: 1rem 0;
  text-align: center;
  color: #555;
}

.level-1:nth-child(odd) {
  background: rgba(244, 49, 11, 0.5);
}

.level-1:nth-child(even){
  background: rgba(250, 231, 179, 0.5);
}

.level-2:nth-child(odd){
  background: rgba(20, 231, 179, 0.5);
}

.level-2:nth-child(even){
  background: rgba(123, 222, 22, 0.5);
}

.full {
  margin-top: 1rem;
  background: rgba(123, 222, 22, 0.5);
}

h2 {
  padding: 1rem 0;
  text-align: center;
  color: #555;
}

.gallery {
  @include cf;
  
  &__item {
    @include cf;
    @include nested(6){
      @include gallery(2)
    }
  }
  
  &__subitem {
    @include nested(2) {
      @include gallery(1);
      /*
      @include span(1);
      &:last-child {
        @include last;
      }
      */
    }
  }
}

SassMeister-output.css

*, *:before, *:after {
  -moz-box-sizing: border-box;
  box-sizing: border-box;
}

img, video {
  max-width: 100%;
  height: auto;
}

:root {
  font-family: sans-serif;
}

ul, ol, li {
  margin: 0;
  padding: 0;
}

li {
  list-style: none;
}

.wrap {
  max-width: 1140px;
  margin-left: auto;
  margin-right: auto;
  background-image: linear-gradient(to right, rgba(102, 102, 255, 0.25), rgba(179, 179, 255, 0.25) 80%, transparent 80%);
  background-size: 12.82051%;
  background-origin: content-box;
  background-clip: content-box;
  background-position: left top;
}

.wrap:after {
  content: " ";
  display: block;
  clear: both;
}

.content {
  margin-top: 10vh;
  background: rgba(113, 218, 210, 0.8);
  width: 74.35897%;
  float: left;
  margin-right: 2.5641%;
}

.sidebar {
  margin-top: 10vh;
  background: rgba(250, 231, 179, 0.8);
  width: 23.07692%;
  float: right;
  margin-right: 0;
}

.sidebar a {
  color: #666;
  padding-left: 1rem;
  line-height: 2;
  text-decoration: none;
}

h2 {
  padding: 1rem 0;
  text-align: center;
  color: #555;
}

.level-1:nth-child(odd) {
  background: rgba(244, 49, 11, 0.5);
}

.level-1:nth-child(even) {
  background: rgba(250, 231, 179, 0.5);
}

.level-2:nth-child(odd) {
  background: rgba(20, 231, 179, 0.5);
}

.level-2:nth-child(even) {
  background: rgba(123, 222, 22, 0.5);
}

.full {
  margin-top: 1rem;
  background: rgba(123, 222, 22, 0.5);
}

h2 {
  padding: 1rem 0;
  text-align: center;
  color: #555;
}

.gallery:after {
  content: " ";
  display: block;
  clear: both;
}

.gallery__item {
  width: 31.03448%;
  float: left;
}

.gallery__item:after {
  content: " ";
  display: block;
  clear: both;
}

.gallery__item:nth-child(3n + 1) {
  margin-left: 0;
  margin-right: -100%;
  clear: both;
  margin-left: 0;
}

.gallery__item:nth-child(3n + 2) {
  margin-left: 34.48276%;
  margin-right: -100%;
  clear: none;
}

.gallery__item:nth-child(3n + 3) {
  margin-left: 68.96552%;
  margin-right: -100%;
  clear: none;
}

.gallery__subitem {
  width: 44.44444%;
  float: left;
  /*
      @include span(1);
      &:last-child {
        @include last;
      }
      */
}

.gallery__subitem:nth-child(2n + 1) {
  margin-left: 0;
  margin-right: -100%;
  clear: both;
  margin-left: 0;
}

.gallery__subitem:nth-child(2n + 2) {
  margin-left: 55.55556%;
  margin-right: -100%;
  clear: none;
}

SassMeister-rendered.html

<div class='wrap'>
  <div class='content'>
    <h2>Content</h2>
    <div class='gallery'>
      <div class='gallery__item level-1'>
        <h2>Item 1</h2>
        <div class='gallery__subitem level-2'>
          <h2>SubItem 3</h2>
        </div>
        <div class='gallery__subitem level-2'>
          <h2>SubItem 4</h2>
        </div>
      </div>
      <div class='gallery__item level-1'>
        <h2>Item 2</h2>
        <div class='gallery__subitem level-2'>
          <h2>SubItem 1</h2>
        </div>
        <div class='gallery__subitem level-2'>
          <h2>SubItem 2</h2>
        </div>
      </div>
      <div class='gallery__item level-1'>
        <h2>Item 3</h2>
      </div>
      <div class='full'>
        <h2>Full Wide Item</h2>
      </div>
    </div>
  </div>
  <div class='sidebar'>
    <h2>
      Sidebar
    </h2>
  </div>
</div>