- add padding
- add stopping on every page
- change selected index recognition

#579

SInce this is a non-Material element the font is not automatically 
inherited. Needs to be done explicitly.

#574

- Minuend instead Subtrahend is strikable

#571

#578

An error was made in the last release. Now the numbers are correct.

#574

#560

style used in other cloze children causes the error
':host {display:flex !important; width: 100%; height: 100%;}'

-> Don't hive line-coloring input but just disable.

#558

#559

The former solution was affecting the selection CSS of the button. Now 
the text is moved down instead.

#562

#542

This is much smaller and the intended way for web apps.

#457
#539

The directive for dynamic backgroudn color was outdated. Directive is 
removed and problem is solved via CSS custom variable.

#561

Explicitly define a label to be shown, since the shown label is done via 
innerHTML.

Gridsizes were accidentally changed from array to object.

The ClozeDocument was not cloned properly. Since it is possibly 
infinitely nested, manual reconstruction is less viable.

#449

- position
- label
- icon

- Replace throwing Errors with InstantiationErors in unit, page and
  section in strictInstantiation mode

#548