CiviCRM 5.21.0 with Drupal 7
I set up an event registration and added some custom fields and set the width to be smaller than default (usually 20 or 30 wide).
In the preview from the Registration tab of the event the fields look correct, but when displayed on the actual page the fields extend the whole width of the page - even though you can still only enter the set maximum number of characters in that huge field.
The "canned" fields from the Individual profile do not do this - they display the expected length. It's just the custom fields I created that run the full width of the page.