Fieldset template should have the "ecl-form-group" class

[arismag]

Fieldset template should have the "ecl-form-group" class set on:

oe_theme/templates/form/fieldset.html.twig

This how it is set on ecl. If left as is, the fieldset element inherits browser style.

In any case an implementation as on oe_theme/templates/form/select.html.twig is really helpful in such cases since you override only the classes and not the full template, so it's more likely not to lose anything and next updates.

{# Set default wrapper classes. #}
{# This also allows overriding templates to take control of classes like width modifiers. #}
{% set wrapper_classes = wrapper_classes|default([
  'ecl-select__container',
  'ecl-select__container--m',
]) %}