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/svelte/src/lib/container/Pane/Pane.svelte

@@ -203,20 +203,10 @@
 
 <style>
   .svelte-flow__pane {
-    cursor: grab;
     position: absolute;
     top: 0;
     left: 0;
     width: 100%;
     height: 100%;
-    z-index: 1;
-  }
-
-  .selection {
-    cursor: pointer;
-  }
-
-  .dragging {
-    cursor: grabbing;
   }
 </style>