Icons are made similar to the Breeze theme icons,
The window magnification and window reduction icons are now different,
the picture on the icons are made transparent.
Sorry for the extended review time for this! Next time, posting both before and after screenshots might be helpful for people not familiar with the current UI. Anyway, it looks good to me. Let's also see what @Zren says, since he's rapidly becoming the de facto maintainer of this code. :)
We're currently trying to draw the C++ Breeze/forks window decorations in T9899 (and https://bugs.kde.org/show_bug.cgi?id=399757), which would make these SVGs obsolete. However we can merge these in the short term until that code is ready.
Oddly enough, the previous SVGs didn't follow the color scheme (nor do the new ones but thats fine).