Temporary show small popup with custom text whenever someone enters page

Hi there,

i was wondering if it is somehow possible to show a custom popup announcement somewhere on a gp page - like on the top.
I want to have the possibility to give small announcements like "meet us at some fair in hall 2". on the landing page.
The note can then be closed via an x or ok-button or something. It would also be a temporary thing i would want to be able to disable/change.

Couldn't find something - but maybe i am not searching with the right terms.

Any hints, links or ideas?