This may work for you or at least get you started.
.templatePicker .grid .dojoxGridCell {background-color:transparent; border-color: transparent;}
.templatePicker .grid .dojoxGridRow {background-color: transparent; border-color: transparent;}
.templatePicker .grid .dojoxGridRowOver .dojoxGridCell {background-color:transparent}
.templatePicker .grid .dojoxGridRowOdd {background-color: transparent;}
.dojoxGridScrollbox {background-color: transparent;}
.templatePicker {background-color: transparent;}
.templatePicker .grid {background-color: transparent;}