space-y-* and space-x-* aliases use padding instead of margin

[chrismurrph]

The space-y-* and space-x-* aliases generate padding rules instead of margin rules, which doesn't match Tailwind's behaviour.

Current (shadow-css 0.6.4):

(:space-y-1 (:aliases (shadow.css.build/start)))
;; => [["& > * + *" {:padding-top "0.25rem", :padding-bottom "0.25rem"}]]

Expected (matching Tailwind):

;; => [["& > * + *" {:margin-top "0.25rem"}]]

Two problems: (1) padding instead of margin — space-y-* should add spacing between children via margin-top, not expand padding. (2) Sets both top and bottom — this overrides any py-* already on the child element, since both target the same properties.

Same issue affects space-x-* (uses padding-left/padding-right instead of margin-left).

Workaround:

(update build-state :aliases merge
  {:space-y-1 [["& > * + *" {:margin-top "0.25rem"}]]
   :space-x-8 [["& > * + *" {:margin-left "2rem"}]]})

Reproduced on 0.4.6 and 0.6.4.