This is the one

SassMeister-input-HTML.html

<div id="content">
 <div id="topmenu">Top Menu</div>
  <div id="main_menu_container">
    <div id="logo">Logo</div>
    <div id="mainmenu">Main Menu</div>
  </div>
  <div id="hero">
    <div id="main_hero">Main Hero</div>
    <div id="hero_grid">
      <div class="hero_grid_item" id="hero_grid_item1">Hero 1</div>
      <div class="hero_grid_item" id="hero_grid_item2">Hero 2</div>
      <div class="hero_grid_item" id="hero_grid_item3">Hero 3</div>
    </div>
  </div>
  <div id="showcase_grid">
    <div class="showcase_item" id="showcase_item1">Showcase 1</div>
    <div class="showcase_item" id="showcase_item2">Showcase 2</div>
    <div class="showcase_item" id="showcase_item3">Showcase 3</div>
  </div>
</div>
<div id="footer">Such Footer</div>

SassMeister-input.scss

// ----
// Sass (v3.4.4)
// Compass (v1.0.1)
// Breakpoint (v2.5.0)
// Susy (v2.1.3)
// ----

@import "susy";
@import "breakpoint";
@import "compass/reset";

@mixin clearfix() {
    &:before,
    &:after {
        content: "";
        display: table;
    }
    &:after {
        clear: both;
    }
}

$susy: (
  columns: 12,
	debug: (
		image: show,
		color: blue,
		output: background,
		toggle: top right,
	)
);

html, body {
  height: 100%;
}

#content {
  height: 100%;
  background-color: #000;
  bottom: 0;
  @include container();

  #main_menu_container {
    background-color: #fff;
    @include clearfix();
    @include span(12 of 12);
  }
  
  #hero {
    background-color: #f00;
    @include span(12 of 12);
    #hero_grid {
      @include span(12 of 12);
      @include clearfix();
      
      .hero_grid_item {
        float: left;
        background-color: #f0f;
        @include span(4 of 12);
        @include bleed;
      }
      
      #hero_grid_item3 {
        @include omega;
      }
    }
  }
    
  #showcase_grid {
    background-color: #fff;
    @include clearfix();
    width: span(10);
    margin: 0 auto;
    
    .showcase_item {
      float: left;
      background-color: #0f0;
      @include span(4);
      @include bleed;
    }
    
    #showcase_item3 {
      @include omega;
    }
  }
}

  #footer {
    background-color: yellow;
    position: relative;
    min-height: 200px;
    margin-top: -200px;
    bottom: 0;
  }

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;
}

html, body {
  height: 100%;
}

#content {
  height: 100%;
  background-color: #000;
  bottom: 0;
  max-width: 100%;
  margin-left: auto;
  margin-right: auto;
  background-image: linear-gradient(to right, blue, #4d4dff 80%, transparent 80%);
  background-size: 8.47458%;
  background-origin: content-box;
  background-clip: content-box;
  background-position: left top;
}
#content:after {
  content: " ";
  display: block;
  clear: both;
}
#content #main_menu_container {
  background-color: #fff;
  width: 100%;
  float: left;
  margin-left: 0;
  margin-right: 0;
}
#content #main_menu_container:before, #content #main_menu_container:after {
  content: "";
  display: table;
}
#content #main_menu_container:after {
  clear: both;
}
#content #hero {
  background-color: #f00;
  width: 100%;
  float: left;
  margin-left: 0;
  margin-right: 0;
}
#content #hero #hero_grid {
  width: 100%;
  float: left;
  margin-left: 0;
  margin-right: 0;
}
#content #hero #hero_grid:before, #content #hero #hero_grid:after {
  content: "";
  display: table;
}
#content #hero #hero_grid:after {
  clear: both;
}
#content #hero #hero_grid .hero_grid_item {
  float: left;
  background-color: #f0f;
  width: 32.20339%;
  float: left;
  margin-right: 1.69492%;
  margin-right: -1.69492%;
  margin-left: -1.69492%;
  padding-right: 1.69492%;
  padding-left: 1.69492%;
}
#content #hero #hero_grid #hero_grid_item3 {
  float: right;
  margin-right: 0;
}
#content #showcase_grid {
  background-color: #fff;
  width: 83.05085%;
  margin: 0 auto;
}
#content #showcase_grid:before, #content #showcase_grid:after {
  content: "";
  display: table;
}
#content #showcase_grid:after {
  clear: both;
}
#content #showcase_grid .showcase_item {
  float: left;
  background-color: #0f0;
  width: 32.20339%;
  float: left;
  margin-right: 1.69492%;
  margin-right: -1.69492%;
  margin-left: -1.69492%;
  padding-right: 1.69492%;
  padding-left: 1.69492%;
}
#content #showcase_grid #showcase_item3 {
  float: right;
  margin-right: 0;
}

#footer {
  background-color: yellow;
  position: relative;
  min-height: 200px;
  margin-top: -200px;
  bottom: 0;
}

SassMeister-rendered.html

<div id="content">
 <div id="topmenu">Top Menu</div>
  <div id="main_menu_container">
    <div id="logo">Logo</div>
    <div id="mainmenu">Main Menu</div>
  </div>
  <div id="hero">
    <div id="main_hero">Main Hero</div>
    <div id="hero_grid">
      <div class="hero_grid_item" id="hero_grid_item1">Hero 1</div>
      <div class="hero_grid_item" id="hero_grid_item2">Hero 2</div>
      <div class="hero_grid_item" id="hero_grid_item3">Hero 3</div>
    </div>
  </div>
  <div id="showcase_grid">
    <div class="showcase_item" id="showcase_item1">Showcase 1</div>
    <div class="showcase_item" id="showcase_item2">Showcase 2</div>
    <div class="showcase_item" id="showcase_item3">Showcase 3</div>
  </div>
</div>
<div id="footer">Such Footer</div>