feat(styles): one stylesheet source for react and svelte (#3350)

* feat(styles): create stylesheets for react and svelte based on one source

* refactor(styling): cleanup

* refactor(postcss): share a config

* refactor(postcss): replace env hack with env file

packages/react/src/styles/utils.ts

@@ -0,0 +1,9 @@
+import type { CSSProperties } from 'react';
+
+export const containerStyle: CSSProperties = {
+  position: 'absolute',
+  width: '100%',
+  height: '100%',
+  top: 0,
+  left: 0,
+};