fix(modal): add explicit margin auto to dialog element styles (#3312)

* fix(modal): add explicit margin

* chore(modal): changeset

Author: stephl3

.changeset/cruel-frogs-accept.md

@@ -0,0 +1,7 @@
+---
+'@leafygreen-ui/modal': patch
+'@leafygreen-ui/confirmation-modal': patch
+'@leafygreen-ui/marketing-modal': patch
+---
+
+Add explicit `margin: auto;` to `<dialog>` element styles to prevent `margin` property being reset

packages/modal/src/Modal/Modal.styles.ts

@@ -59,6 +59,7 @@ const getBaseDialogStyles = (theme: Theme) => css`
   background-color: ${color[theme].background[Variant.Primary][
     InteractionState.Default
   ]};
+  margin: auto;
   padding: ${spacing[1000]}px ${spacing[900]}px;
   color: ${color[theme].text[Variant.Primary][InteractionState.Default]};
   font-family: ${fontFamilies.default};