Problem with look and feel after installing LXDE

[Mario Castelán Castro]

Hello.

I installed LXDE in Debian 8 in a virtual machine from a text-only 
environment using "aptitude -R". I had to install a display manager 
separately to have a working graphic environment; I installed "lightdm" 
with aptitude (without "-R").

I found that some programs, such as the one responsible for the shutdown 
menu and Qt programs (like KAlarm) have a very plain look and feel (like 
that of Windows 95) which is inconsistent with the rest of the system 
(that has a more polished look and feel). I'd like to make these 
programs have the same look and feel as the rest of the system.

As a test, I installed "lxde" in a different virtual machine *without* 
the "-R" option. The shutdown menu has the right look and feel, 
consistent with the rest of the system. Therefore, I think that the "-R" 
option is making the installation lack the package responsible for this 
look and feel, so the question is: what is that package?, or otherwise, 
how can I make the programs that have the plain look and feel look the 
same as the rest of the system (like Iceweasel).

Thanks in advance.