I'm assuming that you are using DotNetNuke v 7.x. One of the default.css changes in DNN 7.x was to change the DNN 6.x required field indicator from a red bar on the left border of input and textarea tags to a small "star" to beside the field label. As Feedback has not yet been updated to follow the new DNN 7 form patterns it applies the class "dnnFormRequired" to any field element that is defined in the module settings as being required. In DNN 7.x, the "dnnFormRequired" class has to be applied to the filed label (dnnLabel control or label html tag).
You should be able to restore the DNN 6.x style required field indicators by adding the following CSS rules to those in the file DesktopModules/Feedback/module.css:
.FeedbackForm input.dnnFormRequired, .NarrowFeedbackForm input.dnnFormRequired,
.FeedbackForm textarea.dnnFormRequired, .NarrowFeedbackForm textarea.dnnFormRequired
{
border-left:5px #F00 solid;
}
.FeedbackForm .dnnFormHelp p.dnnFormRequired,
.NarrowFeedbackForm .dnnFormHelp p.dnnFormRequired
{
border-left: 5px #F00 solid;
padding-left: 5px;
}
I don't believe there is a purely css fix that would apply the DNN 7.x pattern's red "star" on required field labels should you prefer that approach.
I'm not personally in favor of the change to required field indicators in DNN 7.x so have been adding the above to some existing site's Feedback modules as they are upgraded to DNN 7.x.