You can control circle and rounded icons with .rounded, .rounded-2x and .rounded-x classes.
Now, you can control icons sizes very easily with predefined WowUI classes such as .icon-lg and .icon-sm
You are able to use more than 10 predefined icon color styeles and you can also make your icon stlyes. Moreover, you can creat unlimeted block styles using WowUI Icon Styles. Here are some more awesome examples.
.rounded class to make rounded icon style. For circle icons you should add .rounded-x class.