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

package.json

@@ -10,10 +10,11 @@
   ],
   "private": true,
   "scripts": {
+    "postinstall": "preconstruct dev && yarn run packages",
     "dev": "preconstruct watch",
     "dev:example": "cd examples/nextjs && yarn dev",
-    "postinstall": "preconstruct dev",
-    "build": "preconstruct build",
+    "build": "preconstruct build && yarn run packages",
+    "packages": "yarn workspaces foreach --include '@react-flow/**' run build",
     "test:all": "yarn test:chrome && yarn test:firefox",
     "test:chrome": "cypress run --browser chrome",
     "test:firefox": "cypress run --browser firefox",
@@ -29,10 +30,7 @@
     "@babel/preset-react": "^7.17.12",
     "@babel/preset-typescript": "^7.17.12",
     "@preconstruct/cli": "^2.1.8",
-    "autoprefixer": "^10.4.7",
     "cypress": "^10.3.1",
-    "postcss": "^8.4.14",
-    "postcss-nested": "^5.0.6",
     "start-server-and-test": "^1.14.0",
     "typescript": "^4.7.4"
   },