This is the SCSS partial I use to initialize all of my newly created Bourbon/Neat projects. Requires http://bourbon.io/ and http://neat.bourbon.io/

_init.css.scss

/////////////////////////////////////////////////////////////////////
//                                                                 //
//  INITIALIZE  ················································   //
//                                                                 //
//  put all non-directly compiled, globally required CSS here      //
//  (variables, mixins, librabry includes like bourbon/neat, etc)  //
//                                                                 //
//  add "@import 'init';" to the top of every scss partial         //
//                                                                 //
/////////////////////////////////////////////////////////////////////

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


//// VARIABLES ////

// colors

// typography


//// MIXINS ////

// css-arrow mixin
// use:
// @include css-arrow(right, center, 20px, 0, #ddd, #aaa, flag);
@mixin css-arrow($box-edge         : bottom,
                 $edge-side        : center,
                 $arrow-size       : 10px,
                 $edge-side-offset : 0,
                 $fill-color       : black,
                 $border-color     : none,
                 $border-style     : border) {

// initiate internal variables
  $box-edge-inverse: bottom;
  $edge-side-pos: $edge-side;
  $edge-side-pos-value: 0;

// establish inverse variables
  @if      $box-edge == top    { $box-edge-inverse: bottom; }
  @else if $box-edge == right  { $box-edge-inverse: left;   }
  @else if $box-edge == bottom { $box-edge-inverse: top;    }
  @else if $box-edge == left   { $box-edge-inverse: right;  }

// calculate remaining internal variables
  @if ($box-edge == 'top' or
       $box-edge == 'bottom') {
    @if $edge-side == center {
      $edge-side-pos: left;
      $edge-side-pos-value: 50%;
      $edge-side-offset: (-$arrow-size);
    }
  }
  @if ($box-edge == 'left' or
       $box-edge == 'right') {
    @if $edge-side == center {
      $edge-side-pos: top;
      $edge-side-pos-value: 50%;
      $edge-side-offset: (-$arrow-size);
    }
  }

  &:after, &:before {
    content: " ";
    height: 0;
    width: 0;
    position: absolute;
    pointer-events: none;
    border: solid rgba(#fff, 0);
  }

  &:after  {
    border-color: rgba(#fff, 0);
    border-width: $arrow-size - 1;
    #{$box-edge}: (-$arrow-size) - $arrow-size + 2;
    border-#{$box-edge-inverse}-color: $fill-color;
    #{$edge-side-pos}: $edge-side-pos-value;
    margin-#{$edge-side-pos}: $edge-side-offset + 1;
  }

  @if $border-style == flag {
    @include border-radius(2px);
    &:before {
      border-color: rgba(#fff, 0);
      border-width: $arrow-size - 1;
      #{$box-edge}: (-$arrow-size) - $arrow-size + 2;
      border-#{$box-edge-inverse}-color: $border-color;
      #{$edge-side-pos}: $edge-side-pos-value;
      margin-#{$edge-side-pos}: $edge-side-offset + 2;
    }
  } @else {
    &:before {
      border-color: rgba(#fff, 0);
      border-width: $arrow-size;
      #{$box-edge}: (-$arrow-size) - $arrow-size;
      border-#{$box-edge-inverse}-color: $border-color;
      #{$edge-side-pos}: $edge-side-pos-value;
      margin-#{$edge-side-pos}: $edge-side-offset;
    }
  }
}

@mixin fill($width: 100%) {
  @include box-sizing(border-box);
  width: $width;
}

@mixin font-smoothing($value: on) {
    @if $value == on {
        -webkit-font-smoothing: antialiased;
        -moz-osx-font-smoothing: grayscale;
    }
    @else {
        -webkit-font-smoothing: subpixel-antialiased;
        -moz-osx-font-smoothing: auto;
    }
}