$timing-fn-default: cubic-bezier(0.4, 0, 0.2, 1);
$timing-fn-linear: linear;
$timing-fn-in: cubic-bezier(0.4, 0, 1, 1);
$timing-fn-out: cubic-bezier(0, 0, 0.2, 1);
$timing-fn-in-out: cubic-bezier(0.4, 0, 0.2, 1);

$duration-default: 150ms;