How can I change the scrollbar width in kde plasma 5.9.4 ubuntu 17.04. The Application Style dialog box no longer contains this setting. I’m old and they are too small.
I don’t know about 17.04, but in 18.04 you can select the Oxygen style, which has a setting for the scrollbar width. The default Breeze does not.
For gtk applications I created my own theme in ~/.themes based on an existing one in /usr/share/themes and modified gtk.css to make the scrollbar larger. This is easier with gtk-3.20 than with previous versions, you just have to increase some min-width in the Scrollbars section, and optionally the border-radius. In 3.18 and earlier you have to increase the stretch dimensions for many elements, in the same file.
Still, I wish developers would just use at least 20 pixels for a scrollbar by default, it’s not too much out of 1920 pixels and these are well spent pixels…