With the recently introduced Common Styles, we are now adding styles to fragments in a div that wraps them.
As a consequence, it was not possible to completely remove the bottom margin for some fragments that included <p> or <h1> tags, that have a margin by default. A ticket was created for it: https://issues.liferay.com/browse/LPS-120942. To fix it, we added mb-0 class to Heading and HTML fragments.
It could be a problem for pages created on 7.2 using the old version of the fragments, as for that cases we may remove the margin.
For that reason, we should adapt the Upgrade process so old fragments don't lose the margin when upgrading to 7.3.