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/controls/src/ControlButton.tsx

@@ -0,0 +1,22 @@
+import React, { FC, PropsWithChildren } from 'react';
+import cc from 'classcat';
+
+import { ControlButtonProps } from './types';
+
+const ControlButton: FC<PropsWithChildren<ControlButtonProps>> = ({
+  children,
+  className,
+  ...rest
+}) => (
+  <button
+    type="button"
+    className={cc(['react-flow__controls-button', className])}
+    {...rest}
+  >
+    {children}
+  </button>
+);
+
+ControlButton.displayName = 'ControlButton';
+
+export default ControlButton;