Kicker block's influence on adjacent block's margin being overridden

[douglas-johnson]

In #90 we added default vertical spacing within wp-block-column

This is overriding the reduced margin that we apply using .wp-block-cata-kicker + *

We can win the specificity fight pretty easily with !important

We could also refactor how our version of .stack works to use CSS custom properties similar to the Every Layout version or this Flow and Rhythm example from CUBE CSS:
https://cube.fyi/composition.html#flow-and-rhythm
https://every-layout.dev/layouts/stack/

.wp-block-cata-kicker + * {
  --space: 0.375em;
}