In older versions of typo3(up to 6.2.x) we have had an options to add section frames to each content elements to have different classes for the elements.
In TYPO3 7.x this feature is removed but the same is added again in TYPO3 8.x.
Here is the code on how you can add it
TCEFORM.tt_content.frame_class.addItems {
content-boxWrapper = Content Box
}
This is renders as following in front end
<div id="c100" class="frame frame-content-boxWrapper frame-type-list frame-layout-0">
now you can style it with the class .frame-content-boxWrapper{}