Generated by SassMeister.com.

SassMeister-input-HTML.html

<div class="vanity">
  <div class="focus">
    <h2>Hello World</h2>
  </div>
</div>

SassMeister-input.scss

// ----
// Sass (v3.3.5)
// Compass (v1.0.0.alpha.18)
// Bitters (v)
// Bourbon (v)
// Neat (v)
// ----

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

@mixin flexbox( $display: flex, $direction: row, $wrap: wrap, $justify: start, $items: start, $content: start ) {
// <display> - flex | inline-flex
// <direction> - row | row-reverse | column | column-reverse
// <wrap> - wrap | nowrap | wrap-reverse
// <justify> - start | end | center | space-between | space-around
// <items> - start | end | center | baseline | stretch
// <content> - start | end | center | space-between | space-around | stretch

// @include flexbox( flex, row, wrap, start, start, start );
// @include flexbox( inline-flex, column, nowrap, center, start, stretch );
// @include flexbox( flex, row-reverse, wrap, center, start, center );

  @-moz-document url-prefix() {
      -moz-box-sizing: border-box;
      width: 100%;
  }

  display: -webkit-box;
  display: -moz-box;
  display: -ms-#{$display}box;
  display: -webkit-#{$display};
  display: $display;

@if $direction == row {
  -webkit-box-direction: normal;
  -moz-box-direction: normal;
  -webkit-box-orient: horizontal;
  -moz-box-orient: horizontal;
} @else if $direction == row-reverse {
  -webkit-box-direction: reverse;
  -moz-box-direction: reverse;
  -webkit-box-orient: horizontal;
  -moz-box-orient: horizontal;
} @else if $direction == column {
  -webkit-box-direction: normal;
  -moz-box-direction: normal;
  -webkit-box-orient: vertical;
  -moz-box-orient: vertical;
} @else if $direction == column-reverse {
  -webkit-box-direction: reverse;
  -moz-box-direction: reverse;
  -webkit-box-orient: vertical;
  -moz-box-orient: vertical;
}

  -webkit-flex-direction: $direction;
  -ms-flex-direction: $direction;
  flex-direction: $direction;

  -webkit-flex-wrap: $wrap;
  -ms-flex-wrap: $wrap;
  flex-wrap: $wrap;

@if $justify == start {
  -webkit-box-pack: $justify;
  -moz-box-pack: $justify;
  -webkit-justify-content: flex-#{$justify};
  -ms-flex-pack: $justify;
  justify-content: flex-#{$justify};
} @else if $justify == end {
  -webkit-box-pack: $justify;
  -moz-box-pack: $justify;
  -webkit-justify-content: flex-#{$justify};
  -ms-flex-pack: $justify;
  justify-content: flex-#{$justify};
} @else if $justify == space-between {
  -webkit-box-pack: justify;
  -moz-box-pack: justify;
  -webkit-justify-content: $justify;
  -ms-flex-pack: justify;
  justify-content: $justify;
} @else if $justify == space-around {
  -webkit-box-pack: justify;
  -moz-box-pack: justify;
  -webkit-justify-content: $justify;
  -ms-flex-pack: distribute;
  justify-content: $justify;
} @else {
  -webkit-box-pack: $justify;
  -moz-box-pack: $justify;
  -webkit-justify-content: $justify;
  -ms-flex-pack: $justify;
  justify-content: $justify;
}

@if $items == start {
  -webkit-box-align: $items;
  -moz-box-align: $items;
  -webkit-align-items: flex-#{$items};
  -ms-flex-align: $items;
  align-items: flex-#{$items};
} @else if $items == end {
  -webkit-box-align: $items;
  -moz-box-align: $items;
  -webkit-align-items: flex-#{$items};
  -ms-flex-align: $items;
  align-items: flex-#{$items};
} @else {
  -webkit-box-align: $items;
  -moz-box-align: $items;
  -webkit-align-items: $items;
  -ms-flex-align: $items;
  align-items: $items;
}

@if $content == start {
  -webkit-align-content: flex-#{$content};
  -ms-flex-line-pack: $content;
  align-content: flex-#{$content};
} @else if $content == end {
  -webkit-align-content: flex-#{$content};
  -ms-flex-line-pack: $content;
  align-content: flex-#{$content};
} @else if $content == space-between {
  -webkit-align-content: $content;
  -ms-flex-line-pack: justify;
  align-content: $content;
} @else if $content == space-around {
  -webkit-align-content: $content;
  -ms-flex-line-pack: distribute;
  align-content: $content;
} @else {
  -webkit-align-content: $content;
  -ms-flex-line-pack: $content;
  align-content: $content;
}
}

@mixin flex( $grow: 0, $shrink: 1, $basis: auto ) {
// <grow> - flex-grow (integer)
// <shrink> - flex-shrink (integer)
// <basis> - flex-basis (length)

// @include flex( 0, 1, auto );
// @include flex( 2, 1, 100px );

  -webkit-box-flex: $grow;
  -moz-box-flex: $grow;
  -webkit-flex: $grow $shrink $basis;
  -ms-flex: $grow $shrink $basis;
  flex: $grow $shrink $basis;
}

@mixin flexitem( $order: 0, $grow: 0, $shrink: 1, $basis: auto, $align: auto ) {
// <order> -(integer)
// <grow> - flex-grow (integer)
// <shrink> - flex-shrink (integer)
// <basis> - flex-basis (length)
// <align> - start | end | center | space-between | space-around | stretch

// @include flexitem( 0, 0, 1, auto, start );
// @include flexitem( 1, 1, 1, 100px, stretch );
// @include flexitem( 0, 2, 1, auto, center );

  -webkit-box-ordinal-group: $order + 1;
  -moz-box-ordinal-group: $order + 1;
  -webkit-order: $order;
  -ms-flex-order: $order;
  order: $order;

  @include flex( $grow, $shrink, $basis );

  -webkit-align-self: $align;
  -ms-flex-item-align: $align;
  align-self: $align;
}

.vanity {
  height:10em;
  background:rgb(160,160,160);
  @include flexbox(flex,column,start,center,start); // i'd use bourbon 4 if it were avail
  text-align:center;
  color:white;
}

.focus {
  background:purple;
  @include flex(0,0);
  width:100%;
}

h2 {
  line-height:140%;
}

SassMeister-output.css

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

button,
input[type="submit"] {
  border: 1px solid #2459a6;
  border-radius: 3px;
  box-shadow: inset 0 1px 0 0 #89a8d5;
  color: white;
  display: inline-block;
  font-size: inherit;
  font-weight: bold;
  background-color: #477dca;
  background-image: -webkit-linear-gradient(#477dca, #2760b2);
  background-image: linear-gradient(#477dca, #2760b2);
  padding: 7px 18px;
  text-decoration: none;
  text-shadow: 0 1px 0 #1b4f9a;
  background-clip: padding-box;
  font-size: 1em;
}
button:hover:not(:disabled),
input[type="submit"]:hover:not(:disabled) {
  box-shadow: inset 0 1px 0 0 #628cc8;
  cursor: pointer;
  background-color: #3c71bb;
  background-image: -webkit-linear-gradient(#3c71bb, #255aa5);
  background-image: linear-gradient(#3c71bb, #255aa5);
}
button:active:not(:disabled),
input[type="submit"]:active:not(:disabled) {
  border: 1px solid #2459a6;
  box-shadow: inset 0 0 8px 4px #235397, inset 0 0 8px 4px #235397, 0 1px 1px 0 #eeeeee;
}
button:disabled,
input[type="submit"]:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

body {
  color: #333333;
  font-family: "Helvetica Neue", Helvetica, Roboto, Arial, sans-serif;
  font-size: 1em;
  -webkit-font-smoothing: antialiased;
  line-height: 1.5em;
}

h1, h2, h3, h4, h5, h6 {
  font-family: "Helvetica Neue", Helvetica, Roboto, Arial, sans-serif;
  line-height: 1.25em;
  margin: 0;
  text-rendering: optimizeLegibility;
}

h1 {
  font-size: 2.25em;
}

h2 {
  font-size: 2em;
}

h3 {
  font-size: 1.75em;
}

h4 {
  font-size: 1.5em;
}

h5 {
  font-size: 1.25em;
}

h6 {
  font-size: 1em;
}

p {
  margin: 0 0 0.75em;
}

a {
  color: #477dca;
  text-decoration: none;
  -webkit-transition: color 0.1s linear;
  -moz-transition: color 0.1s linear;
  transition: color 0.1s linear;
}
a:hover {
  color: #2c5999;
}
a:active, a:focus {
  color: #2c5999;
  outline: none;
}

hr {
  border-bottom: 1px solid #dddddd;
  border-left: none;
  border-right: none;
  border-top: none;
  margin: 1.5em 0;
}

img {
  margin: 0;
  max-width: 100%;
}

abbr, acronym {
  border-bottom: 1px dotted #dddddd;
  cursor: help;
}

address {
  display: block;
  margin: 0 0 0.75em;
}

hgroup {
  margin-bottom: 0.75em;
}

del {
  color: #595959;
}

blockquote {
  border-left: 2px solid #dddddd;
  color: #595959;
  margin: 1.5em 0;
  padding-left: 0.75em;
}

cite {
  color: #737373;
  font-style: italic;
}
cite:before {
  content: '\2014 \00A0';
}

fieldset {
  background: #f7f7f7;
  border: 1px solid #dddddd;
  margin: 0 0 0.75em 0;
  padding: 1.5em;
}

input,
label,
select {
  display: block;
  font-family: "Helvetica Neue", Helvetica, Roboto, Arial, sans-serif;
  font-size: 1em;
}

label {
  font-weight: bold;
  margin-bottom: 0.375em;
}
label.required:after {
  content: "*";
}
label abbr {
  display: none;
}

textarea,
input[type="email"], input[type="number"], input[type="password"], input[type="search"], input[type="tel"], input[type="text"], input[type="url"], input[type="color"], input[type="date"], input[type="datetime"], input[type="datetime-local"], input[type="month"], input[type="time"], input[type="week"] {
  -webkit-box-sizing: border-box;
  -moz-box-sizing: border-box;
  box-sizing: border-box;
  -webkit-transition: border-color;
  -moz-transition: border-color;
  transition: border-color;
  background-color: white;
  border-radius: 0.1875em;
  border: 1px solid #dddddd;
  box-shadow: inset 0 1px 3px rgba(0, 0, 0, 0.06);
  font-family: "Helvetica Neue", Helvetica, Roboto, Arial, sans-serif;
  font-size: 1em;
  margin-bottom: 0.75em;
  padding: 0.5em 0.5em;
  resize: vertical;
  width: 100%;
}
textarea:hover,
input[type="email"]:hover, input[type="number"]:hover, input[type="password"]:hover, input[type="search"]:hover, input[type="tel"]:hover, input[type="text"]:hover, input[type="url"]:hover, input[type="color"]:hover, input[type="date"]:hover, input[type="datetime"]:hover, input[type="datetime-local"]:hover, input[type="month"]:hover, input[type="time"]:hover, input[type="week"]:hover {
  border-color: #c4c4c4;
}
textarea:focus,
input[type="email"]:focus, input[type="number"]:focus, input[type="password"]:focus, input[type="search"]:focus, input[type="tel"]:focus, input[type="text"]:focus, input[type="url"]:focus, input[type="color"]:focus, input[type="date"]:focus, input[type="datetime"]:focus, input[type="datetime-local"]:focus, input[type="month"]:focus, input[type="time"]:focus, input[type="week"]:focus {
  border-color: #477dca;
  box-shadow: inset 0 1px 3px rgba(0, 0, 0, 0.06), 0 0 5px rgba(55, 112, 192, 0.7);
  outline: none;
}

input[type="search"] {
  -webkit-appearance: none;
  -moz-appearance: none;
  -ms-appearance: none;
  -o-appearance: none;
  appearance: none;
}

input[type="checkbox"], input[type="radio"] {
  display: inline;
  margin-right: 0.375em;
}

input[type="file"] {
  width: 100%;
}

select {
  width: auto;
  margin-bottom: 1.5em;
}

button,
input[type="submit"] {
  -webkit-appearance: none;
  -moz-appearance: none;
  -ms-appearance: none;
  -o-appearance: none;
  appearance: none;
  cursor: pointer;
  user-select: none;
  vertical-align: middle;
  white-space: nowrap;
}

table {
  border-collapse: collapse;
  margin: 0.75em 0;
  table-layout: fixed;
  width: 100%;
}

th {
  border-bottom: 1px solid #b7b7b7;
  font-weight: bold;
  padding: 0.75em 0;
  text-align: left;
}

td {
  border-bottom: 1px solid #dddddd;
  padding: 0.75em 0;
}

tr, td, th {
  vertical-align: middle;
}

ul, ol {
  margin: 0;
  padding: 0;
  list-style-type: none;
}
dl {
  line-height: 1.5em;
  margin-bottom: 0.75em;
}
dl dt {
  font-weight: bold;
  margin-top: 0.75em;
}
dl dd {
  margin: 0;
}

.error, #flash_failure {
  background: #fbe3e4;
  color: #96151b;
  font-weight: bold;
  margin-bottom: 0.75em;
  padding: 0.75em;
}
.error a, #flash_failure a {
  color: #6a0f13;
}
.error a:hover, #flash_failure a:hover {
  color: #110203;
}

.notice, #flash_notice {
  background: #fff6bf;
  color: #8c7800;
  font-weight: bold;
  margin-bottom: 0.75em;
  padding: 0.75em;
}
.notice a, #flash_notice a {
  color: #594c00;
}
.notice a:hover, #flash_notice a:hover {
  color: black;
}

.success, #flash_success {
  background: #e6efc2;
  color: #56651a;
  font-weight: bold;
  margin-bottom: 0.75em;
  padding: 0.75em;
}
.success a, #flash_success a {
  color: #333c10;
}
.success a:hover, #flash_success a:hover {
  color: black;
}

.vanity {
  height: 10em;
  background: #a0a0a0;
  display: -webkit-box;
  display: -moz-box;
  display: -ms-flexbox;
  display: -webkit-flex;
  display: flex;
  -webkit-box-direction: normal;
  -moz-box-direction: normal;
  -webkit-box-orient: vertical;
  -moz-box-orient: vertical;
  -webkit-flex-direction: column;
  -ms-flex-direction: column;
  flex-direction: column;
  -webkit-flex-wrap: start;
  -ms-flex-wrap: start;
  flex-wrap: start;
  -webkit-box-pack: center;
  -moz-box-pack: center;
  -webkit-justify-content: center;
  -ms-flex-pack: center;
  justify-content: center;
  -webkit-box-align: start;
  -moz-box-align: start;
  -webkit-align-items: flex-start;
  -ms-flex-align: start;
  align-items: flex-start;
  -webkit-align-content: flex-start;
  -ms-flex-line-pack: start;
  align-content: flex-start;
  text-align: center;
  color: white;
}
@-moz-document url-prefix() {
  .vanity {
    -moz-box-sizing: border-box;
    width: 100%;
  }
}
.focus {
  background: purple;
  -webkit-box-flex: 0;
  -moz-box-flex: 0;
  -webkit-flex: 0 0 auto;
  -ms-flex: 0 0 auto;
  flex: 0 0 auto;
  width: 100%;
}

h2 {
  line-height: 140%;
}

SassMeister-rendered.html

<div class="vanity">
  <div class="focus">
    <h2>Hello World</h2>
  </div>
</div>