I think the site looks great and is very useful. The one suggestion I have would be to add a bit of space to everything to give it some breathing room.

These are the changes I made: try them out and see what you think.

body { padding: 10px; background: #f0f0f0; }

#groups { grid-template-columns: repeat(auto-fill, minmax(350px, 1fr)); }

.group { padding: 10px; margin: 4px; }

.group > span { margin: 0 20px 20px 0; }

.gmatch { padding: 6px 0; }