Delete `box-sizing` global override

[fateeand]

There is a global override of box-sizing in cps-ui-kit/styles/styles.scss, that lives there from the beginning:

*,
*::before,
*::after {
  box-sizing: border-box;
}

Even though this is extremely common and generally considered a best practice in app-level CSS, this is a violation of the library boundary, and we need to delete it, leaving it up to the consuming apps whether to apply it.

It's already applied in the composition app, so it should simply be removed from the library.
If some components hardly depend on border-box, it should be applied locally within the component scope.