Alternate row colors & add timestamp on check event

How can I do this for a repeating panel? I don’t understand css but following your example, i tried

.anvil-panel-col:nth-child(even) {
background: %color:Gray 200%;;
}

works

but

.anvil-panel-row:nth-child(even) {
background: %color:Gray 200%;;
}

does not work