How to change KDE Plasma scrollbar width?

How can I change the scrollbar width in KDE Plasma 5.9.4 on Ubuntu 17.04?

The Application Style dialog box no longer contains this setting.


In KUbuntu 20.04 I found by changing some numbers in: /usr/share/themes/Breeze/gtk-3.0

Towards the end, in my case lines starting at line 38456, fixed my problem.

scrollbar trough {
    transition-duration: 0.1s;
    min-width: 20px;
}

and

scrollbar:hover trough {
    background-color: mix(@theme_unfocused_bg_color,@theme_unfocused_fg_color,0.7);
    min-width: 18px;
}
scrollbar:hover slider {
    min-width: 18px;
}