just-the-docs/node_modules/primer-support/lib/variables/layout.scss

// Layout variables
// stylelint-disable declaration-bang-space-before

// These are our margin and padding utility spacers. The default step size we
// use is 8px. This gives us a key of:
//    0 => 0px
//    1 => 4px
//    2 => 8px
//    3 => 16px
//    4 => 24px
//    5 => 32px
//    6 => 40px
$spacer: 8px !default;
$spacers: (
  0,
  round($spacer / 2),
  $spacer,
  $spacer * 2,
  $spacer * 3,
  $spacer * 4,
  $spacer * 5
) !default;

// Aliases for easy use
$spacer-0: nth($spacers, 1) !default; // 0
$spacer-1: nth($spacers, 2) !default; // 4px
$spacer-2: nth($spacers, 3) !default; // 8px
$spacer-3: nth($spacers, 4) !default; // 16px
$spacer-4: nth($spacers, 5) !default; // 24px
$spacer-5: nth($spacers, 6) !default; // 32px
$spacer-6: nth($spacers, 7) !default; // 40px

// Em spacer variables
$em-spacer-1: 0.0625em !default; // 1/16
$em-spacer-2: 0.125em !default;  // 1/8
$em-spacer-3: 0.25em !default;   // 1/4
$em-spacer-4: 0.375em !default;  // 3/8
$em-spacer-5: 0.5em !default;    // 1/2
$em-spacer-6: 0.75em !default;   // 3/4

// Fixed-width container variables
$container-width: 980px !default;
$grid-gutter:     10px !default;

// Breakpoint widths
$width-xs: 0;
$width-sm: 544px;
$width-md: 768px;
$width-lg: 1012px;
$width-xl: 1280px;

// Responsive container widths
$container-md: $width-md !default;
$container-lg: $width-lg !default;
$container-xl: $width-xl !default;

// Breakpoints
$breakpoints: (
  // Small screen / phone
  sm: $width-sm,
  // Medium screen / tablet
  md: $width-md,
  // Large screen / desktop (980 + (16 * 2)) <= container + gutters
  lg: $width-lg,
  // Extra large screen / wide desktop
  xl: $width-xl
) !default;

$responsive-variants: ("": "");
@each $key in map-keys($breakpoints) {
  $responsive-variants: map-merge($responsive-variants, ($key: "-#{$key}"));
}