Can't make round corners

Hello,

This is the best table plugin!!!

I’m trying to make my corners round.
I found this code and paste it in my child theme css and nothing hapens. 🙁
I’m doing something wrong?

.tablepress thead th:first-child {
border-top-left-radius: 10px;
}
.tablepress thead th:last-child {
border-top-right-radius: 10px;
}
.tablepress tbody tr:last-child td:first-child {
border-bottom-left-radius: 10px;
}
.tablepress tbody tr:last-child td:last-child {
border-bottom-right-radius: 10px;
}

https://ww.wp.xz.cn/plugins/wp-table-reloaded/