It would be good to add a high z-index to .flag-message, as well as a background color and possibly padding and border. Reason is that if a bookmark is at the edge of a container, the flag message is partially hidden. By adding this CSS it will show on top of the bordering containers.

This is the CSS I have used to override .flag-message:

z-index: 20; background: #ffffff; padding: 0.2em; border: 1px solid #e3e3e3; text-align: left;