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/css-utils/src/index.ts

@@ -0,0 +1,10 @@
+export function injectStyle(css: string) {
+  if (typeof document === 'undefined') return;
+
+  const head = document.head || document.getElementsByTagName('head')[0];
+  const style = document.createElement('style');
+
+  head.prepend(style);
+
+  style.appendChild(document.createTextNode(css));
+}