Event registration in back office: checkbox not usable

[Detsieber]

See screenshot!

[MegaphoneJon]

@Detsieber I had this problem on D9 with the "Seven" theme, but not with the "Seven Roundearth" theme.

If you're not on D7, Compuco won't provide a fix here, but they might be willing to review a PR. Note that the core team maintains a D9-compatible fork for CiviCRM Spark, but I haven't tested if the problem is present there.