Generated by SassMeister.com.

SassMeister-input-HTML.haml

%header
  %h1 Flexbox - ordering items
%h2 Control display with order
%section.flex-container
  .box.one
    %h3 One
  .box.two
    %h3 Two
  .box.three
    %h3 Three
  .box.four
    %h3 Four
%h2 Control display with flex-flow & justify-content
%section.flex-container.reverse
  .box
    %h3 One
  .box
    %h3 Two
  .box
    %h3 Three
  .box
    %h3 Four
%h2 Control nested display
%section.flex-container
  .box
    %h3 One
  .box
    %h3 Two
    %section.flex-container.nested
      .box
        %h3 One
      .box
        %h3 Two
      .box
        %h3 Three
      .box.four
        %h3 Four
  .box
    %h3 Three
  .box
    %h3 Four

SassMeister-input.scss

// ----
// Sass (v3.3.0.rc.2)
// Compass (v1.0.0.alpha.17)
// ----

@import "compass";
@import url(http://fonts.googleapis.com/css?family=Audiowide);

// Documentation about Flex
// http://www.w3.org/TR/css3-flexbox/

$colors: (chartreuse, royalblue, plum, teal, lightsteelblue, sienna, maroon, lime, cornflowerblue, darkviolet, dodgerblue);

@for $n from 1 through length($colors) {
  .box:nth-child(#{$n}) {
    background-color: nth($colors, $n);
  }
}

body {
  width: 80%;
  margin: 0 auto;
  padding: 2%;
  line-height: 1.6;
}

.flex-container {
  @include display-flex(flex);

  border: 1px solid #333;

  // flex-flow is a shorthand for flex-direction & flex-wrap
  @include flex-flow(row);
  
  &.reverse {
    @include flex-flow(row-reverse);
    @include justify-content(flex-end);
  }
  
  &.nested {
    @include flex-flow(column);
    .box {
      font-size: 1em;
    }
  }
}

.box {
  color: #222;
  font-family: 'Audiowide', cursive;
  font-size: 1.8em;
  line-height: 1;
  padding: 10px 20px;
  text-align: center;
  text-shadow: 0 -1px 0 #fefefe;
}
.one {
  @include order(4);
}
.two {
  @include order(3);
}
.three {
  @include order(2);
}
.four {
  @include order(1);
  .nested & {
    @include order(-1);
  }
}

SassMeister-output.css

@import url(http://fonts.googleapis.com/css?family=Audiowide);
.box:nth-child(1) {
  background-color: chartreuse;
}

.box:nth-child(2) {
  background-color: royalblue;
}

.box:nth-child(3) {
  background-color: plum;
}

.box:nth-child(4) {
  background-color: teal;
}

.box:nth-child(5) {
  background-color: lightsteelblue;
}

.box:nth-child(6) {
  background-color: sienna;
}

.box:nth-child(7) {
  background-color: maroon;
}

.box:nth-child(8) {
  background-color: lime;
}

.box:nth-child(9) {
  background-color: cornflowerblue;
}

.box:nth-child(10) {
  background-color: darkviolet;
}

.box:nth-child(11) {
  background-color: dodgerblue;
}

body {
  width: 80%;
  margin: 0 auto;
  padding: 2%;
  line-height: 1.6;
}

.flex-container {
  display: -webkit-flex;
  display: flex;
  border: 1px solid #333;
  -webkit-flex-flow: row;
  flex-flow: row;
}
.flex-container.reverse {
  -webkit-flex-flow: row-reverse;
  flex-flow: row-reverse;
  -webkit-justify-content: flex-end;
  justify-content: flex-end;
}
.flex-container.nested {
  -webkit-flex-flow: column;
  flex-flow: column;
}
.flex-container.nested .box {
  font-size: 1em;
}

.box {
  color: #222;
  font-family: 'Audiowide', cursive;
  font-size: 1.8em;
  line-height: 1;
  padding: 10px 20px;
  text-align: center;
  text-shadow: 0 -1px 0 #fefefe;
}

.one {
  -webkit-order: 4;
  order: 4;
}

.two {
  -webkit-order: 3;
  order: 3;
}

.three {
  -webkit-order: 2;
  order: 2;
}

.four {
  -webkit-order: 1;
  order: 1;
}
.nested .four {
  -webkit-order: -1;
  order: -1;
}

SassMeister-rendered.html

<header>
  <h1>Flexbox - ordering items</h1>
</header>
<h2>Control display with order</h2>
<section class='flex-container'>
  <div class='box one'>
    <h3>One</h3>
  </div>
  <div class='box two'>
    <h3>Two</h3>
  </div>
  <div class='box three'>
    <h3>Three</h3>
  </div>
  <div class='box four'>
    <h3>Four</h3>
  </div>
</section>
<h2>Control display with flex-flow & justify-content</h2>
<section class='flex-container reverse'>
  <div class='box'>
    <h3>One</h3>
  </div>
  <div class='box'>
    <h3>Two</h3>
  </div>
  <div class='box'>
    <h3>Three</h3>
  </div>
  <div class='box'>
    <h3>Four</h3>
  </div>
</section>
<h2>Control nested display</h2>
<section class='flex-container'>
  <div class='box'>
    <h3>One</h3>
  </div>
  <div class='box'>
    <h3>Two</h3>
    <section class='flex-container nested'>
      <div class='box'>
        <h3>One</h3>
      </div>
      <div class='box'>
        <h3>Two</h3>
      </div>
      <div class='box'>
        <h3>Three</h3>
      </div>
      <div class='box four'>
        <h3>Four</h3>
      </div>
    </section>
  </div>
  <div class='box'>
    <h3>Three</h3>
  </div>
  <div class='box'>
    <h3>Four</h3>
  </div>
</section>