Sweet theme: large borders around windows when up-scaling in system settings

[rageblob]

Hello everyone,
this is my first time using github, so sorry in advance for any mistakes made.
I started using Sweet theme for KDE Plasma 5 on my Kubuntu 18.04 machine today.

I got a 4k display today and after setting the scaling factor to 1.5 in system settings, there now are these huge dark borders around open windows.
No idea where they're coming from, but it's quite irritating.

Here's a screenshot of the problem in action.

Hopefully the issue is easy to fix.
Thanks for your attention.

[EliverLara]

Hi, please take a look at #34, I thinks it's the same issue