re: But when I tried to change the border color from #d3d3d3 to #5c2c81 in all the css files, nothing changes.
tile-plus.min.css file and make the change to the
tile-plus.css and then force refresh your browser so the browser downloads the new version rather than using the browser’s locally cached version.
re: I then tried to add “border: 1px solid #5c2c81;” to the shortcode, but still nothing changed.
Remove that from the shortcode the template/Connections does not have that as an available option and it could break the shortcode, keep it from working right.
Hope that helps! Let me know!