I managed to figure it out! Playing around with the styling options, I realized that the color of the large border around the avatars was matching the color of the text for that section. So I added this code to the section to make the color match the background of my page and it worked!
COPY CODE
.activity-avatar
{
color:#f0f0f0;
}
.rounded
{
color:#f0f0f0;
}