Semantic UI applications include hundreds of references to SUI classes in well-defined patterns. Trying to translate them all to Bootstrap would be a very large effort, so we introduced a backwards-compatibility layer of CSS definitions to keep some of them them in place.
To use it copy sui-compatibility.css to the src/main/angular/src directory of your application, then add
@import "./sui-compatibility.css";
to styles.css.
The compatibility layer can be expanded as needed. The current version allows re-using the following patterns:
<div class="ui left icon input">
<i class="some icon"></i>
...
</div>
where some icon should be replaced by some-translated sui-icon.
For instance,
<i class="calendar icon"></i>
becomes
<i class="far fa-calendar-alt sui-icon"></i>
See Migrating Icons from Semantic UI for the icon migration rules.