According to documentation if you have this situation:
<div th:include="..."> content here </div>
fragment will be placed inside <div> tag.
However when you use replace:
<div th:replace="..."> content here </div>
then <div> will be replaced by content.
Thymeleaf can include parts of other pages as fragments (whereas JSP
only includes complete pages) using th:include (will include the
contents of the fragment into its host tag) or th:replace (will
actually substitute the host tag by the fragment’s).