The specification does not explicitly state this, but the sources around w3.org seem to indicate that fieldsets should be styled using border-* properties to set the borders needed.
The HTML5 working draft offers default styles for the fieldset element, which browsers can use in their default style implementations. You can see the border style used here.
fieldset { margin-left: 2px; margin-right: 2px; border: groove 2px ThreeDFace; padding: 0.35em 0.625em 0.75em; }
This would mean that the error in IE and Opera should be reported by Microsoft and Opera ASA respectively. I'm not too sure though, again, W3C never said anything about border-radius (or border-image ). You can always try to file bug reports and see what each provider says.
UPDATE: since dstorey (an Opera employee) notes in a comment, this is a known bug in Opera.
source share