Java vs C++ GUI libraries?

Java vs C++ GUI libraries?

I am currently working on a project that is a SaaS. All functionality to
the end user is only available with an internet connection by accessing a
website currently. However, this is troublesome because the software is a
management software that won't have wifi in range at all times for the
users to connect to. For this reason, I am trying to develop a software
with similar functionality to the online SaaS that will basically be an
offline version of the online site. I must be able to use mySQL.
So I'd like to start with understanding what styling options are there
with various Java or C++ (I would consider other languages as well)
libraries and how complex would it be to develop a GUI with drop down
menus, auto fill capabilities, box shadows, background colors. Ideally any
library that resembles CSS in its capabilities is a plus.
I appreciate any advice, many thanks in advance!