osTicket is not themeable at this time. So you would need to edit (Modify) the core files to achieve a custom look.
There are several third party theme mods that you could take a look at. See the Themes section on this:
https://tmib.net/resources-for-osticket/
Thanks for the information.
I've been telling the devs that for... ummm... longer than i can remember,
ntozier ... and the devs are ... defs? *g sorry :-)
very punny. 
ntozier This manual too general. Any tutorial how to custom staff themes?
Currently osTicket does not have themes. A "Theme" would be a Mod.
Once osTicket is officially themeable there will likely be better guides.
Paid themes : https://www.osticketresponsivetheme.com/
Free Themes : https://github.com/philbertphotos/osticket-bootstrap-theme
jlinkson could you check the datepicker part of the theme. i think it is not showing up.
gammybear
I think that this is a bug in 1.15.8, as the arrows to go back and forward in selection of months do now show of with te built-in theme either.
1.15.x is no longer supported so I would highly suggest upgrading to one of the latest, supported versions; v1.16.5 or v1.17.2. However, you may need this:
Cheers.
