Referring to this Office Hours Post: adding
.AnswersVerticalGrid .Hitchhiker-2-columns .yxt-Card-child, .AnswersVerticalGrid .Hitchhiker-3-columns .yxt-Card-child, .AnswersVerticalGrid .Hitchhiker-4-columns .yxt-Card-child {
border: none;
}
to the answers.scss file but outside the .answers {} did the trick! Thanks @Kristy_Huang!