How change icon checkbox from component p:selectOneRadio primefaces?

I need to change icon checked from component primefaces selectOneRadio, below the component code:

        <p:selectOneRadio value="#{item.listaAtividadesSelecionadas}" 
          rendered="#{item.habilitarItens}"
            layout="grid" columns="1"  >
            <f:selectItems value="#{item.listaAtividades}" />
        </p:selectOneRadio>

I already try to override de CSS primefaces class but I couldn't. Please anyone has a simple solution?