Table row groups

I have a requirement that every third row needs to be highlighted. It does not seem like I can do this via code by adding a class to the specific row nor is there a grouping feature that would allow to do this. I am hoping not to have to create a list of rows with either odd or even in my css file to make up for this. Does anyone know if this is possible?

I was able to figure it out using CSS:

.v-table-mainTable .v-table-row:nth-of-type(3n) .v-table-cell-content,
.v-table-mainTable .v-table-row-odd:nth-of-type(3n) .v-table-cell-content {
      -stuff-
}