With a focus on being "light-weight", it is to KDE Plasma what XFCE is to GNOME: a familiar enough looking lighter alternative to the more fully featured environment that may work better on lower-end devices and for people who want as lean a system as possible.
As all Qt desktop environments themeing is hard since you need to know C++ , there is a sideway using qss however its not as powerful as GTK, Enlightenment or Windows theming.
In the current state, LXQT is a beta desktop that feels like a heavy alpha. A lot of the tools and underlying features are in a testing state, while the LXQT project itself has not had a gold (1.0.0) release as of yet.