Issue with link hover color

First thanks for a vastly improved system over Jetpack comments. It's even better with the up front moderation add-on I purchased.

Second, I'm pulling my hair out over what should be a simple problem to solve. I've tried suggested solutions posted in the forum to no avail.

The problem is that when commenters leave a link, the hover-over color turns white, making the link text invisible. While the link still works fine, less technically tolerant people get a bit freaked out.

You can see what I'm talking about in this thread:  https://wattsupwiththat.com/2018/06/open-thread-trying-out-a-new-comment-system/

I've added this bit of custom CSS to the "styling" section of the WPDISCUZ settings...which should make the hover over red...

#wpcomm input[type="submit"]:hover{
border: 1px solid #DD0000 !important;;
background-color: #DD0000 !important;;
}

But it does.....nothing, nothing at all.

I'm about as fluent in CSS as I am in Swahili, and it makes no sense to me why this won't work.

Help, please.