CSS3 variables

### References

https://codepen.io/antoniococe/pen/vYKrJxz

```
  "scripts": {
    "start": "json-server --watch db.json"
  },
```

`curl --header "Content-Type: application/json"   --X POST   -d '{"username":"xyz","password":"xyz"'   http://localhost:3000/posts`