That's just the browser's default styling for the
<dfn>
tag.
You can either override the default styling, or use a tag with no default style, like
<span>
.
Span:
✯
Dfn with inline style:
✯
Span: <span title="star">✯</span>
Dfn with inline style: <dfn title="star" style="font-style:normal;">✯</dfn>