Problem/Motivation
The css definition for .claro-details overrides any .hidden class on the element.
Steps to reproduce
In a hook_form_alter() add an `[#attribute][class][] = hidden` on an element of [#type] = `details` gets overridden by the .claro-details { display: block} definition.
Proposed resolution
Does the `.claro-details` definition need the `display: block`? Drupal's default is for `details` to display as `block`.
Remaining tasks
Possibly all that is required is to remove the display: block from the .claro-details definition.
