Find where you installed the Seated listings in your site code and add this style block just before.
<style>
.seated-event-link1,
.seated-event-link1:visited,
.seated-event-link2,
.seated-event-link2:visited {
border-color: rgba(255, 255, 255, 1) !important;
}
</style>
Note: This makes the border color white. You can read more about rgba() here. You can pick your own color here, and just add the opacity you want to the end of the color.