[1.3.x] updated core.css - added some z-w widths

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes minor
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | -
| Fixed tickets | -
| Refs tickets  | -
| License       | MIT
| Doc PR        | -

Added some extra widths in the core.css. 100% was missing as z-w100 specification to keep it consistent and 68/32 as golden rule was missing. That is being used quite a bit in Content as width division.