Refactor: CSS handling (#2344)

* refactor(css): only load base styles, add css task, cleanup exports
* style(base): add edge label bg
* refactor(css): use css-utils
* feat(core): add Panel component
* refactor(background): cleanup
* refactor(css-handling): cleanup

packages/minimap/src/style.ts

@@ -0,0 +1,6 @@
+const style = `
+.react-flow__minimap {
+  background-color: #fff;
+}`;
+
+export default style;