$ sudo apt-get update
$ sudo apt-get install kwin-style-qtcurve 

kwin-style-qtcurve is installed in your system.

Make ensure the kwin-style-qtcurve package were installed using the commands given below,

$ sudo dpkg-query -l | grep kwin-style-qtcurve *

You will get with kwin-style-qtcurve package name, version, architecture and description in a table

kwin-style-qtcurve package basic information: