_settings.bootstrap.scss

// optional prefix to prevent naming collisions
$prefix: '';

/*
Bootstrap 4 alpha currently uses 1rem as the base size for sizes.
@see https://github.com/twbs/bootstrap/blob/v4-dev/scss/_variables.scss
If you want to start using this sizes today, use our version
*/
$spacer: 1rem !default;

// sizes
$xxxs: $spacer * 0.2;  // no official bootstrap size
$xxs:  $spacer * 0.25; // no official bootstrap size
$xs:   $spacer * 0.5;
$s:    $spacer * 1.0;
$m:    $spacer * 1.5;
$l:    $spacer * 3.0;
$xl:   $spacer * 4.5;
$xxl:  $spacer * 6.0; // no official bootstrap size
$xxxl: $spacer * 8.0; // no official bootstrap size

// naming delimiters
$delimiter1: '-';
$delimiter2: '-';

// other naming
$a: 'a'; // all values (top, right, bottom, left);
$h: 'x'; // horizontal values (left, right)
$v: 'y'; // vertical values (top, bottom)
$auto: 'auto';
$null: '0';
$neg: '-neg';

$sizes: ( 
  auto: auto, // no official bootstrap size
  "0" : 0,
  xxxs: $xxxs,
  xxs : $xxs, // no official bootstrap size
  xs  : $xs,
  ''  : $s,
  md  : $m,
  lg  : $l,
  xl  : $xl,
  xxl : $xxl, // no official bootstrap size
  xxxl: $xxxl // no official bootstrap size
);