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/core/src/components/Panel/index.tsx

@@ -0,0 +1,21 @@
+import React, { HTMLAttributes, ReactNode } from 'react';
+import cc from 'classcat';
+
+import { PanelPosition } from '../../types';
+
+export type PanelProps = HTMLAttributes<HTMLDivElement> & {
+  position: PanelPosition;
+  children: ReactNode;
+};
+
+function Panel({ position, children, className, ...rest }: PanelProps) {
+  const positionClasses = `${position}`.split('-');
+
+  return (
+    <div className={cc(['react-flow__panel', className, ...positionClasses])} {...rest}>
+      {children}
+    </div>
+  );
+}
+
+export default Panel;