* Tasks
  - (x) Hydrate existing elements instead of re-creating
  - (x) `load-cssx` functions
  - (x) `get-variable`
  - (x) `update-variable`
  - (x) Use css units for `delay` function
  - (x) Specify node type - `button(id)` or `button#id`
  - (x) attributes
  - ( ) `--cssx-text` (and maybe `--cssx-html`?)
  - ( ) Improve error messages
  - ( ) Evaluate `calc`?
  - ( ) `list` & `tuple` data structures?