How do I underline the parent page but not children in nav?

Hi all…still learning!
I have figured how to to make my left nav work so there is an underline for the page that the user is on, which is great.

I am having trouble figuring out how, when I select the parent page, to get the child pages to show without being underlined. Right now the children show, but they are all underlined. I think I’m missing something basic I’m sure-

Any advice would be great…thanks!
page example:
https://criticalgolf.com/?page_id=100

In the stylesheet I am using:
li.current_page_item{
background:#FFFFFF;
}

li.current_page_item a{
text-decoration:underline;
}