Third party icon packs can't theme minimize, maximize & close buttons of gtk3 apps when using Mint-Y theme

[HamzehTamimi]

Here is example of themed buttons on some apps:

But on ther apps it is not themed:

The cause of this is a line in /usr/share/themes/Mint-Y-(Whatever viariant)/gtk-3.0/gtk.css

-gtk-icon-theme: "Mint-Y";

in:

headerbar button.titlebutton.minimize,
.titlebar button.titlebutton.close,
.titlebar button.titlebutton.maximize,
.titlebar button.titlebutton.minimize {
-gtk-icon-theme: "Mint-Y";
background-color: transparent;
background-size: 18px 18px;
background-position: center;
background-repeat: no-repeat;
border-width: 0; }