1. Goto http://slashdot.org using Opera (any version, platform)
2. Hover the tags below the articles.
Tag highlight show using rounded corners.
No rounded corners. See screenshot.
In http://images.slashdot.org/idlecore-tidied.css?T_2_5_0_250
we encounter
.tag-display ul,.tag-display span.tag,.tag-display .tmenu,.tag-display .tmenu li,.tag-display h1.legend{border:0 solid transparent;-moz-border-radius:.4em;-webkit-border-radius:.4em;}
It doesn't use the standard 'border-radius' that Opera supports.
Just add 'border-radius' to the code, just like you have '-moz-border-radius' and '-webkit-border-radius' . This will also make it future proof when such feature will be standard across browsers in the future.
The article tag does not have rounded corners in Opera