Joomla Auto Category Breadcrumbs uses CSS classes to let you easy styling.
The module already has two build-it CSS skins, you can use it as example. If you use your own CSS for styling breadcrumbs, turn option
Skin (CSS) to
Custom (no CSS).
The classes you can use in CSS are:
mod-auto-category-breadcrumbs - the root div of breadcrumbs.
mod-auto-category-breadcrumbs-id-XX - the root div of breadcrumbs for Joomla module XX (see it at the Joomla modules page).
value of 'CSS class' option - your custom CSS class applied to root div tag.
breadcrumbs-item - class for every item.
breadcrumbs-item-id-XX - class for all breadcrumbs items (except
home link) where XX is the ID of article it linked to.
home - class for breadcrumbs item linked to home page.
has-child - the item that has subitem (not last in the list).
has-no-child - the item that has not subitem (last in the list).
article - the item linked to article.
category - the item linked to category (its index article).