Ratio

Add 1x2, 2x3, 3x4 and 4x5 to aspect ratios.

SCSS:

$custom-ratios: (
  "1x2": calc(1 / 2 * 100%),  
  "2x3": calc(2 / 3 * 100%),
  "3x4": calc(3 / 4 * 100%),
  "4x5": calc(4 / 5 * 100%)
);
$aspect-ratios: map-merge($aspect-ratios, $custom-ratios);